Investments-Fair Values (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 22,999	$ 23,770
Gross unrealized gains	1,909	1,321
Gross unrealized losses	(112)	(462)
Fair value	24,796	24,629
U.S. government and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	751	920
Gross unrealized gains	65	57
Gross unrealized losses	0	0
Fair value	816	977
Municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	2,045	2,162
Gross unrealized gains	378	292
Gross unrealized losses	(6)	(12)
Fair value	2,417	2,442
Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	18,787	18,069
Gross unrealized gains	1,359	849
Gross unrealized losses	(82)	(414)
Fair value	20,064	18,504
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	302	348
Gross unrealized gains	39	36
Gross unrealized losses	0	0
Fair value	341	384
ABS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	509	1,443
Gross unrealized gains	3	5
Gross unrealized losses	(13)	(28)
Fair value	499	1,420
RMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	319	406
Gross unrealized gains	45	49
Gross unrealized losses	(3)	(4)
Fair value	361	451
CMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	272	409
Gross unrealized gains	18	31
Gross unrealized losses	(8)	(4)
Fair value	282	436
Redeemable preferred stock
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	14	13
Gross unrealized gains	2	2
Gross unrealized losses	0	0
Fair value	$ 16	$ 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
-SubTopic 10
-Section 50
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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