Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Common shares, par value (in dollars per share)	$ 0.01	$ 0.01
Common shares, shares authorized	1,250,000,000	1,250,000,000
Common shares, shares issued	309,399,529	303,757,574
Treasury shares	105,456,535	81,814,591
Consolidated Investment Entities
Receivables, fair value (in dollars)	$ 77	$ 39
Debt, fair value (in dollars)	4,450	4,712
Other liabilities, fair value (in dollars)	$ 166	$ 85