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	$ 1	$ (3)	$ (5)
Other Net Realized Capital Gains (Losses) | Within fixed maturity investments
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	(18)	(19)	(16)
Other Net Realized Capital Gains (Losses) | Within products
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	(22)	9	(46)
Other Net Realized Capital Gains (Losses) | Designated as Hedging Instrument | Cash Flow Hedging | Interest rate contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	1	1	1
Other Net Realized Capital Gains (Losses) | Designated as Hedging Instrument | Cash Flow Hedging | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	26	2	2
Other Net Realized Capital Gains (Losses) | Designated as Hedging Instrument | Fair Value Hedging | Interest rate contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	0	(3)	(6)
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	1	35	(56)
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	(8)	(4)	6
Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument | Equity contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	61	(11)	(18)
Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument | Credit contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	17	12	3
Policyholder Benefits | Within reinsurance agreements
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	(57)	(25)	125
Held for sale
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	(1,081)	(755)	(48)
Held for sale | Other Net Realized Capital Gains (Losses) | Within fixed maturity investments
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	(5)	(5)	(5)
Held for sale | Other Net Realized Capital Gains (Losses) | Within products
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	203	324	39
Held for sale | Other Net Realized Capital Gains (Losses) | Designated as Hedging Instrument | Cash Flow Hedging | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	10	1	1
Held for sale | 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	125	(6)	137
Held for sale | 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	(38)	91	56
Held for sale | Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument | Equity contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	(1,376)	(1,145)	(277)
Held for sale | Other Net Realized Capital Gains (Losses) | Not Designated as Hedging Instrument | Credit contracts
Derivatives, Fair Value [Line Items]
Net realized gains (losses) on derivatives	$ 0	$ (15)	$ 1