Derivative Instruments - Derivatives - Derivative Balance Sheet Classification (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Notional Amount	$ 11,764	$ 12,730
Fair Value	(47)	(90)
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	27	25
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	74	115
Fixed maturities, available-for-sale
Derivatives, Fair Value [Line Items]
Notional Amount	153	153
Fair Value	0	0
Asset Derivatives	0	0
Liability Derivatives	0	0
Other investments
Derivatives, Fair Value [Line Items]
Notional Amount	9,377	9,957
Fair Value	14	10
Asset Derivatives	19	16
Liability Derivatives	(5)	(6)
Other liabilities
Derivatives, Fair Value [Line Items]
Notional Amount	2,234	2,620
Fair Value	(61)	(100)
Asset Derivatives	8	9
Liability Derivatives	(69)	(109)
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	9,531	10,387
Fair Value	(36)	(77)
Asset Derivatives	26	24
Liability Derivatives	(62)	(101)
Interest rate swaps \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	2,080	2,190
Fair Value	0	0
Asset Derivatives	0	1
Liability Derivatives	0	(1)
Interest rate swaps \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	7,100	7,300
Foreign currency swaps \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	153	153
Fair Value	(11)	(13)
Asset Derivatives	1	0
Liability Derivatives	(12)	(13)
Total cash flow hedges
Derivatives, Fair Value [Line Items]
Notional Amount	2,233	2,343
Fair Value	(11)	(13)
Asset Derivatives	1	1
Liability Derivatives	(12)	(14)
Interest rate swaps and futures \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	8,111	7,986
Fair Value	(51)	(83)
Asset Derivatives	3	7
Liability Derivatives	(54)	(90)
Foreign currency swaps and forwards \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	318	213
Fair Value	0	(1)
Asset Derivatives	1	0
Liability Derivatives	(1)	(1)
Credit derivatives that purchase credit protection \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	8	61
Fair Value	0	1
Asset Derivatives	0	2
Liability Derivatives	0	(1)
Credit derivatives that assume credit risk \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	923	823
Fair Value	14	3
Asset Derivatives	15	3
Liability Derivatives	(1)	0
Credit derivatives in offsetting positions \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	46	1,046
Fair Value	0	2
Asset Derivatives	6	11
Liability Derivatives	(6)	(9)
Equity index swaps and options \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	125	258
Fair Value	1	1
Asset Derivatives	1	1
Liability Derivatives	$ 0	$ 0

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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