Consolidated Statements of Financial Position (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Fixed maturities, available-for-sale	$ 49,501.3	$ 49,006.7
Fixed maturities, trading	868.7	971.7
Equity securities, trading	536.4	404.8
Other investments	2,952.5	2,985.8
Cash and cash equivalents	1,651.9	2,833.9
Other liabilities	6,086.5	6,286.2
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)	452.4	450.3
Common stock, outstanding (in shares)	300.9	301.1
Treasury stock (in shares)	151.5	149.2
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	194.9	214.2
Fixed maturities, trading	132.4	132.4
Equity securities, trading	321.4	207.6
Other investments	90.5	97.8
Other investments measured at fair value under fair value option	89.8	97.5
Cash and cash equivalents	209.1	317.7
Other liabilities	555.4	565.2
Other liabilities measured at fair value under fair value option	$ 97.8	$ 88.4