Derivative Financial Instruments - Net Realized Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	$ 58	$ (46)	$ 151	$ (22)
Credit contracts | Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	1	7	1	11
Interest rate contracts | Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	12	(6)	33	(8)
Foreign exchange contracts | Other Net Realized Capital Gains (Losses) | Designated as Hedging Instrument | Cash Flow Hedging
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	2	1	4	21
Foreign exchange contracts | Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	5	0	3	(3)
Equity contracts | Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	(5)	(5)	(9)	15
Fixed maturities | Other Net Realized Capital Gains (Losses)
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	(5)	(4)	(12)	(9)
Within products | Other Net Realized Capital Gains (Losses)
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	15	(9)	43	(14)
Within reinsurance agreements | Policyholder Benefits
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	$ 33	$ (31)	$ 88	$ (35)