Investments-Fair Values (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 25,306	$ 25,822
Gross unrealized gains	2,658	2,486
Gross unrealized losses	(162)	(191)
Fair value	27,802	28,117
U.S. government and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	552	668
Gross unrealized gains	87	102
Gross unrealized losses	0	0
Fair value	639	770
Municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,109	3,156
Gross unrealized gains	565	520
Gross unrealized losses	(12)	(14)
Fair value	3,662	3,662
Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	19,039	19,465
Gross unrealized gains	1,834	1,670
Gross unrealized losses	(124)	(150)
Fair value	20,749	20,985
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	505	654
Gross unrealized gains	57	81
Gross unrealized losses	0	0
Fair value	562	735
ABS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,052	773
Gross unrealized gains	12	13
Gross unrealized losses	(21)	(21)
Fair value	1,043	765
Residential mortgage-backed securities ("RMBS")
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	518	554
Gross unrealized gains	59	55
Gross unrealized losses	(4)	(4)
Fair value	573	605
CMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	518	538
Gross unrealized gains	41	43
Gross unrealized losses	(1)	(2)
Fair value	558	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

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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