Investments (Net Investment Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$ 5,032	$ 4,952	$ 4,976
Investment expense	(158)	(125)	(117)
Net investment income	4,874	4,827	4,859
Fixed maturity AFS securities [Member] | AFS Securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	4,138	4,079	4,041
Equity AFS securities [Member] | AFS Securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	11	9	9
Trading securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	100	107	125
Mortgage loans on real estate [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	422	395	378
Real estate [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	2	4	7
Policy loans [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	140	152	155
Invested cash [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	14	3	2
Commercial mortgage loan prepayment and bond makewhole premiums [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	120	105	138
Alternative investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	75	88	130
Consent fees [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	5	5	2
Other investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	5	$ 5	(11)
Parent Company [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income	$ 3		$ 1