Investments (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available for Sale Securities
Amortized cost	$ 56,901	$ 56,576
Gross unrealized gains	1,963	1,710
Gross unrealized losses	(208)	(447)
Fair value	58,656	57,839
U.S. government and agencies
Schedule of Available for Sale Securities
Amortized cost	3,363	3,572
Gross unrealized gains	70	74
Gross unrealized losses	(7)	(9)
Fair value	3,426	3,637
Municipal
Schedule of Available for Sale Securities
Amortized cost	7,543	7,116
Gross unrealized gains	336	304
Gross unrealized losses	(24)	(87)
Fair value	7,855	7,333
Corporate
Schedule of Available for Sale Securities
Amortized cost	43,007	42,742
Gross unrealized gains	1,394	1,178
Gross unrealized losses	(150)	(319)
Fair value	44,251	43,601
Foreign government
Schedule of Available for Sale Securities
Amortized cost	1,019	1,043
Gross unrealized gains	34	36
Gross unrealized losses	(6)	(4)
Fair value	1,047	1,075
Asset-backed securities (“ABS”)
Schedule of Available for Sale Securities
Amortized cost	1,237	1,169
Gross unrealized gains	16	13
Gross unrealized losses	(10)	(11)
Fair value	1,243	1,171
Residential mortgage-backed securities (“RMBS”)
Schedule of Available for Sale Securities
Amortized cost	549	651
Gross unrealized gains	96	85
Gross unrealized losses	(4)	(8)
Fair value	641	728
Commercial mortgage-backed securities (“CMBS”)
Schedule of Available for Sale Securities
Amortized cost	163	262
Gross unrealized gains	14	17
Gross unrealized losses	(7)	(9)
Fair value	170	270
Redeemable preferred stock
Schedule of Available for Sale Securities
Amortized cost	20	21
Gross unrealized gains	3	3
Gross unrealized losses	0	0
Fair value	$ 23	$ 24

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
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
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