By Saeed Azhar and Tom Arnold

DUBAI, Nov 5 (Reuters) - The detention of Saudi Arabia's Prince Alwaleed bin Talal, known for his big bets on Citigroup and other top Western companies, could have an impact on billions of dollars of investments around the world.

For many foreigners, Prince Alwaleed - whose net worth has been estimated by Forbes magazine at $17 billion - is the face of Saudi business, appearing frequently on international television and in articles on his investments and lifestyle.

A 2013 Forbes magazine profile described his marble-filled, 420-room Riyadh palace, a private Boeing 747 equipped with a throne, and his 120-acre resort on the edge of the Saudi capital with five homes, five artificial lakes and a mini-Grand Canyon.

He is also known for his outspoken views on politics - making headlines in 2015 when he called Donald Trump a "disgrace" on Twitter during the U.S. election campaign.

Prince Alwaleed's investments, current and future, may now be in doubt after he was detained in an investigation by a new Saudi anti-corruption body.

"There will be questions on what this all means," said a senior executive at a European financial institution, who visited Riyadh late last month to attend a big international conference promoting Saudi Arabia as an investment destination.

"People will be looking at any kind of international holdings of the people who have been arrested, to see what will be the impact."

Aside from a stake in Citigroup, Prince Alwaleed, 62, owns significant stakes in Twitter, ride-hailing firm Lyft and Time Warner.

His investment firm Kingdom Holding - whose share price plunged 10 percent on Sunday in response to news of his detention - recently bought about half of a 31.1 percent stake in Saudi lender Banque Saudi Fransi from France's Credit Agricole.

FINANCE MINISTER'S SON

Prince Alwaleed's father was the kingdom's finance minister during the 1960s. Prince Alwaleed formed Kingdom Holding in 1979, initially pouring money into real estate in Riyadh; in the 1990s he ventured into Wall Street, investing heavily in Citigroup.

He had a close relationship with former Citigroup Chief Executive Sanford "Sandy" Weill, and has nurtured close ties with other Wall Street leaders including Goldman Sachs CEO Lloyd Blankfein.

Prince Alwaleed increased his stake in Citigroup at the height of the global financial crisis a decade ago and he has held on to the stake, saying as recently as last month that he was very happy with the investment.

"He's always been a colourful and unofficial public face of Saudi Arabia, though he has never been a key decision-maker in the kingdom," a Gulf-based businessman said.