Investments (Net Investment Income) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$ 4,801	$ 4,763	$ 4,661
Investment expense	(103)	(111)	(120)
Total net investment income	4,698	4,652	4,541
Fixed maturity securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	3,910	3,842	3,694
Equity securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	6	5	6
Trading securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	147	154	157
Mortgage loans on real estate [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	397	408	424
Real estate [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	16	22	24
Standby Real Estate Equity Commitments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	0	1	1
Policy loans [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	163	165	169
Invested cash [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	4	4	7
Commercial Mortgage Loan Prepayment And Bond Make Whole Premiums [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	48	82	67
Alternative Investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	125	90	93
Consent Fees [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	4	3	8
Other Investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$ (19)	$ (13)	$ 11