Derivative Financial Instruments - Notional and Fair Values (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	$ 434	$ 792
Derivatives, Liability Fair Value	584	667
Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	24,490	32,898
Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	710	692
Equity contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,382	782
Credit contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,983	3,051
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	56	106
Designated as Hedging Instrument | Cash Flow Hedging | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	625	324
Designated as Hedging Instrument | Derivatives | Cash Flow Hedging | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	0	4
Derivatives, Liability Fair Value	0	0
Designated as Hedging Instrument | Derivatives | Cash Flow Hedging | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	0	28
Derivatives, Liability Fair Value	60	7
Not Designated as Hedging Instrument | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	27,482	39,570
Not Designated as Hedging Instrument | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	85	368
Not Designated as Hedging Instrument | Equity contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,526	917
Not Designated as Hedging Instrument | Within fixed maturity investments
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	37	55
Derivatives, Liability Fair Value	0	0
Not Designated as Hedging Instrument | Within products
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	0	0
Derivatives, Liability Fair Value	306	291
Not Designated as Hedging Instrument | Within reinsurance agreements
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	0	0
Derivatives, Liability Fair Value	129	79
Not Designated as Hedging Instrument | Credit contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,983	3,051
Not Designated as Hedging Instrument | Derivatives | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	173	550
Derivatives, Liability Fair Value	58	247
Not Designated as Hedging Instrument | Derivatives | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	0	30
Derivatives, Liability Fair Value	2	27
Not Designated as Hedging Instrument | Derivatives | Equity contracts
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	198	95
Derivatives, Liability Fair Value	19	0
Not Designated as Hedging Instrument | Derivatives | Credit contracts
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	26	30
Derivatives, Liability Fair Value	10	16
Held for sale
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	1,525	992
Derivatives, Liability Fair Value	4,182	3,673
Held for sale | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	27,025	35,444
Held for sale | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	244	1,362
Held for sale | Equity contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	28,131	21,545
Held for sale | Credit contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	431	204
Held for sale | Designated as Hedging Instrument | Cash Flow Hedging | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	18	18
Held for sale | Designated as Hedging Instrument | Cash Flow Hedging | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	227	157
Held for sale | Designated as Hedging Instrument | Derivatives | Cash Flow Hedging | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	0	1
Derivatives, Liability Fair Value	0	0
Held for sale | Designated as Hedging Instrument | Derivatives | Cash Flow Hedging | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	0	12
Derivatives, Liability Fair Value	24	4
Held for sale | Not Designated as Hedging Instrument | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	28,412	38,830
Held for sale | Not Designated as Hedging Instrument | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	17	1,205
Held for sale | Not Designated as Hedging Instrument | Equity contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	34,637	28,043
Held for sale | Not Designated as Hedging Instrument | Within fixed maturity investments
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	11	16
Derivatives, Liability Fair Value	0	0
Held for sale | Not Designated as Hedging Instrument | Within products
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	0	0
Derivatives, Liability Fair Value	3,400	3,499
Held for sale | Not Designated as Hedging Instrument | Credit contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	431	204
Held for sale | Not Designated as Hedging Instrument | Derivatives | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	470	530
Derivatives, Liability Fair Value	88	108
Held for sale | Not Designated as Hedging Instrument | Derivatives | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	0	31
Derivatives, Liability Fair Value	0	12
Held for sale | Not Designated as Hedging Instrument | Derivatives | Equity contracts
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	1,043	399
Derivatives, Liability Fair Value	664	50
Held for sale | Not Designated as Hedging Instrument | Derivatives | Credit contracts
Derivatives, Fair Value [Line Items]
Derivatives, Asset Fair Value	1	3
Derivatives, Liability Fair Value	$ 6	$ 0