Investments-Fair Values (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 23,975	$ 25,822
Gross unrealized gains	1,580	2,486
Gross unrealized losses	(382)	(191)
Fair value	25,173	28,117
U.S. government and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	508	668
Gross unrealized gains	68	102
Gross unrealized losses	0	0
Fair value	576	770
Municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	2,212	3,156
Gross unrealized gains	323	520
Gross unrealized losses	(9)	(14)
Fair value	2,526	3,662
Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	18,198	19,465
Gross unrealized gains	1,045	1,670
Gross unrealized losses	(340)	(150)
Fair value	18,903	20,985
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	387	654
Gross unrealized gains	44	81
Gross unrealized losses	(1)	0
Fair value	430	735
ABS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,737	773
Gross unrealized gains	9	13
Gross unrealized losses	(25)	(21)
Fair value	1,721	765
RMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	439	554
Gross unrealized gains	54	55
Gross unrealized losses	(4)	(4)
Fair value	489	605
CMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	481	538
Gross unrealized gains	34	43
Gross unrealized losses	(3)	(2)
Fair value	512	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