Investments-Fair Values (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 22,963	$ 23,770
Gross unrealized gains	1,902	1,321
Gross unrealized losses	(187)	(462)
Fair value	24,678	24,629
U.S. government and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	600	920
Gross unrealized gains	71	57
Gross unrealized losses	0	0
Fair value	671	977
Municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	2,109	2,162
Gross unrealized gains	405	292
Gross unrealized losses	(6)	(12)
Fair value	2,508	2,442
Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	18,387	18,069
Gross unrealized gains	1,316	849
Gross unrealized losses	(154)	(414)
Fair value	19,549	18,504
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	339	348
Gross unrealized gains	42	36
Gross unrealized losses	0	0
Fair value	381	384
ABS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	844	1,443
Gross unrealized gains	4	5
Gross unrealized losses	(16)	(28)
Fair value	832	1,420
RMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	347	406
Gross unrealized gains	40	49
Gross unrealized losses	(4)	(4)
Fair value	383	451
CMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	324	409
Gross unrealized gains	22	31
Gross unrealized losses	(7)	(4)
Fair value	339	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
-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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