Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
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	303,757,574	301,366,044
Treasury shares	81,814,591	54,668,152
Consolidated Investment Entities:
Receivables, fair value (in dollars)	$ 39	$ 33
Debt, fair value (in dollars)	4,712	5,171
Other liabilities, fair value (in dollars)	$ 85	$ 154