Investments - Sales of Available for Sale Securities (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Gross gains	$ 275	$ 222	$ 219
Gross losses	(113)	(159)	(194)
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Sale proceeds	17,614	9,984	11,161
Gross gains	204	196	177
Gross losses	(90)	(138)	(156)
Equity securities, trading
Schedule of Available-for-sale Securities [Line Items]
Sale proceeds	607	359	733
Gross gains	69	26	35
Gross losses	$ (23)	$ (20)	$ (20)

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

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