Derivative Financial Instruments - Net Realized Gains (Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	$ 37	$ 30	$ (12)
Other Net Realized Capital Gains (Losses) | Fixed maturities
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	(5)	(6)	(4)
Other Net Realized Capital Gains (Losses) | Within products
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	55	12	(52)
Other Net Realized Capital Gains (Losses) | Managed custody guarantees
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	0	1	0
Other Net Realized Capital Gains (Losses) | Designated as Hedging Instrument | Cash flow hedges | Interest rate contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	1	0	1
Other Net Realized Capital Gains (Losses) | Designated as Hedging Instrument | Cash flow hedges | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	12	(2)	1
Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument | Interest rate contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	(7)	50	(16)
Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	(3)	(1)	1
Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument | Equity contract
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	1	1	(1)
Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument | Credit contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	5	3	0
Interest Credited and Other Benefits to Contract Owners | Within reinsurance agreements
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	$ (22)	$ (28)	$ 58