Investments - Appreciation (Depreciation) on Fixed Maturities (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 14,299	$ 15,465
Unrealized Appreciation	1,525	2,254
Unrealized (Depreciation)	(73)	(30)
Total fair value	15,751	17,689
Run-off Settlement Annuity Business [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized Appreciation	614	883
Unrealized (Depreciation)	(12)	(8)
Total fair value	2,800	3,100
Federal government and agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	454	509
Unrealized Appreciation	297	393
Unrealized (Depreciation)	(1)	0
Total fair value	750	902
State and local government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,089	2,169
Unrealized Appreciation	191	270
Unrealized (Depreciation)	(4)	(2)
Total fair value	2,276	2,437
Foreign government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,120	1,197
Unrealized Appreciation	82	126
Unrealized (Depreciation)	(7)	(1)
Total fair value	1,195	1,322
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,707	10,590
Unrealized Appreciation	852	1,308
Unrealized (Depreciation)	(54)	(17)
Total fair value	10,505	11,881
Federal agency mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	92	121
Unrealized Appreciation	1	1
Unrealized (Depreciation)	(1)	0
Total fair value	92	122
Other mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	64	82
Unrealized Appreciation	4	11
Unrealized (Depreciation)	(4)	(4)
Total fair value	64	89
Other asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	773	797
Unrealized Appreciation	98	145
Unrealized (Depreciation)	(2)	(6)
Total fair value	$ 869	$ 936