Investments - Net Investment Income (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 1,166,000,000	$ 1,222,900,000	$ 3,434,600,000	$ 3,536,000,000
Less: Investment expenses	2,400,000	1,300,000	4,500,000	3,500,000
Net investment income	1,163,600,000	1,221,600,000	3,430,100,000	3,532,500,000
Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	1,006,800,000	974,600,000	2,983,900,000	2,967,900,000
Number of investments not producing income	0		0
Equity securities, available-for-sale
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	2,300,000	3,400,000	9,700,000	6,500,000
Mortgage loans on real estate
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	124,200,000	118,500,000	358,500,000	362,200,000
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	28,500,000	29,500,000	84,600,000	89,100,000
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	900,000	800,000	2,400,000	2,700,000
Other
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 3,300,000	$ 96,100,000	$ (4,500,000)	$ 107,600,000