Investments-Fair Values (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 24,767	$ 25,822
Gross unrealized gains	1,865	2,486
Gross unrealized losses	(248)	(191)
Fair value	26,384	28,117
U.S. government and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	690	668
Gross unrealized gains	65	102
Gross unrealized losses	0	0
Fair value	755	770
Municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,090	3,156
Gross unrealized gains	419	520
Gross unrealized losses	(20)	(14)
Fair value	3,489	3,662
Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	18,545	19,465
Gross unrealized gains	1,226	1,670
Gross unrealized losses	(201)	(150)
Fair value	19,570	20,985
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	470	654
Gross unrealized gains	47	81
Gross unrealized losses	(1)	0
Fair value	516	735
ABS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	982	773
Gross unrealized gains	9	13
Gross unrealized losses	(20)	(21)
Fair value	971	765
RMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	477	554
Gross unrealized gains	58	55
Gross unrealized losses	(4)	(4)
Fair value	531	605
CMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	500	538
Gross unrealized gains	38	43
Gross unrealized losses	(2)	(2)
Fair value	536	579
Redeemable preferred stock
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	13	14
Gross unrealized gains	3	2
Gross unrealized losses	0	0
Fair value	$ 16	$ 16