Investments-Fair Values (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 23,135	$ 23,770
Gross unrealized gains	1,616	1,321
Gross unrealized losses	(308)	(462)
Fair value	24,443	24,629
U.S. government and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	856	920
Gross unrealized gains	68	57
Gross unrealized losses	0	0
Fair value	924	977
Municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	2,138	2,162
Gross unrealized gains	342	292
Gross unrealized losses	(9)	(12)
Fair value	2,471	2,442
Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	17,581	18,069
Gross unrealized gains	1,091	849
Gross unrealized losses	(261)	(414)
Fair value	18,411	18,504
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	338	348
Gross unrealized gains	41	36
Gross unrealized losses	0	0
Fair value	379	384
ABS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,432	1,443
Gross unrealized gains	5	5
Gross unrealized losses	(26)	(28)
Fair value	1,411	1,420
RMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	379	406
Gross unrealized gains	41	49
Gross unrealized losses	(5)	(4)
Fair value	415	451
CMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	398	409
Gross unrealized gains	26	31
Gross unrealized losses	(7)	(4)
Fair value	417	436
Redeemable preferred stock
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	13	13
Gross unrealized gains	2	2
Gross unrealized losses	0	0
Fair value	$ 15	$ 15

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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