Investments (Consolidated Variable Interest Entities - Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Proceeds From Securitizations of Loans Held-for-Investment, Carry Value	$ 319
Tax credits guaranteed by third parties that reduce maximum exposure to loss related to other invested assets	117	$ 150
Proceeds from Securitizations of Loans Held-for-investment	339
Financial or other support to investees designated as VIEs	0	0	$ 0
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Assets Obtained As Proceeds In Period	52
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	60,429	$ 60,695
Residential Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 51