Investments - Write Downs and Sales (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pre-Tax Asset Write-downs [Line Items]
Pre-Tax Asset Write-Downs			$ 13	$ 43
Sales Information For Available For Sale Fixed Maturities Equity Securities [Abstract]
Proceeds from sales	$ 516	$ 351	930	712
Gross gains on sales	12	22	59	34
Gross losses on sales	$ 2	$ 1	$ 4	$ 6