Consolidated Statements of Financial Position (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fixed maturities, available-for-sale	$ 49,006.7	$ 48,636.3
Fixed maturities, trading	971.7	1,120.3
Equity securities, trading	404.8	316.9
Other investments	2,988.0	2,641.6
Cash and cash equivalents	2,833.9	1,877.4
Other liabilities	6,286.1	6,143.5
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)	450.3	448.5
Common stock, outstanding (in shares)	301.1	320.4
Treasury stock (in shares)	149.2	128.1
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	214.2	257.9
Fixed maturities, trading	132.4	131.4
Equity securities, trading	207.6	158.6
Other investments	97.8	128.7
Other investments measured at fair value under fair value option	97.5	128.3
Cash and cash equivalents	317.7	100.0
Other liabilities	565.2	433.6
Other liabilities measured at fair value under fair value option	$ 88.4	$ 114.5