Investments (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fixed maturities, available-for-sale:
Gross gains	$ 26,400,000	$ 63,700,000	$ 123,300,000
Gross losses	(158,800,000)	(339,900,000)	(703,900,000)
Other-than-temporary impairment losses on fixed maturities, available-for-sale reclassified to (from) other comprehensive income	(49,700,000)	56,100,000	260,900,000
Hedging, net	130,500,000	142,200,000	(229,100,000)
Fixed maturities, trading	(6,700,000)	17,500,000	49,300,000
Equity securities, available-for-sale:
Gross gains	2,200,000	8,900,000	27,000,000
Gross losses	(6,400,000)	(3,200,000)	(46,500,000)
Equity securities, trading	20,300,000	27,700,000	39,400,000
Mortgage loans	(42,100,000)	(152,200,000)	(153,600,000)
Derivatives	(180,500,000)	(143,900,000)	263,300,000
Other	142,500,000	131,600,000	(28,400,000)
Net realized capital gains (losses)	(122,300,000)	(191,500,000)	(398,300,000)
Proceeds from sales of investments
Proceeds from sales of investments in fixed maturities, available-for-sale	$ 900,000,000	$ 1,600,000,000	$ 3,300,000,000