Consolidated Statements of Financial Position (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fixed maturities, available-for-sale	$ 51,084.1	$ 50,939.3
Fixed maturities, trading	628.9	626.7
Other investments	3,187.2	3,291.1
Other investments measured at fair value under fair value option	110.9	113.9
Separate account assets	120,906.1	81,653.8
Separate account liabilities	120,906.1	81,653.8
Other liabilities	6,130.8	6,146.1
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	2,500.0	2,500.0
Common stock, issued (in shares)	455.9	453.5
Common stock, outstanding (in shares)	293.3	293.8
Treasury stock (in shares)	162.6	159.7
Series A
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, liquidation preference (in dollars per share)	$ 100	$ 100
Preferred stock, authorized (in shares)	3.0	3.0
Preferred stock, issued (in shares)	3.0	3.0
Preferred stock, outstanding (in shares)	3.0	3.0
Series B
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, liquidation preference (in dollars per share)	$ 25	$ 25
Preferred stock, authorized (in shares)	10.0	10.0
Preferred stock, issued (in shares)	10.0	10.0
Preferred stock, outstanding (in shares)	10.0	10.0
Aggregate consolidated variable interest entities
Fixed maturities, available-for-sale	220.3	194.6
Fixed maturities, trading	110.4	110.4
Other investments	77.2	80.3
Separate account assets	33,892.2
Separate account liabilities	33,892.2
Other liabilities	318.3	302.9
Other liabilities measured at fair value under fair value option	$ 96.5	$ 85.0