Derivatives - Derivative Balance Sheet Classification (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Notional Amount	$ 12,730	$ 15,117
Fair Value	(90)	(526)
Asset Derivatives	469	86
Liability Derivatives	(559)	(612)
Fixed maturities, available-for-sale
Derivatives, Fair Value [Line Items]
Notional Amount	153	201
Fair Value	0	1
Asset Derivatives	0	1
Liability Derivatives	0	0
Other investments
Derivatives, Fair Value [Line Items]
Notional Amount	9,957	10,888
Fair Value	10	(415)
Asset Derivatives	448	52
Liability Derivatives	(438)	(467)
Other liabilities
Derivatives, Fair Value [Line Items]
Notional Amount	2,620	4,028
Fair Value	(100)	(112)
Asset Derivatives	21	33
Liability Derivatives	(121)	(145)
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	2,343	1,721
Fair Value	(13)	(85)
Asset Derivatives	94	3
Liability Derivatives	(107)	(88)
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	10,387	13,396
Fair Value	(77)	(441)
Asset Derivatives	375	83
Liability Derivatives	(452)	(524)
Interest rate swaps \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	2,190	1,646
Fair Value	0	(86)
Asset Derivatives	94	2
Liability Derivatives	(94)	(88)
Interest rate swaps \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	7,300	7,900
Foreign currency swaps \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	153	75
Fair Value	(13)	1
Asset Derivatives	0	1
Liability Derivatives	(13)	0
Interest rate swaps and futures \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	7,986	8,969
Fair Value	(83)	(479)
Asset Derivatives	340	15
Liability Derivatives	(423)	(494)
Foreign currency swaps and forwards \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	213	682
Fair Value	(1)	32
Asset Derivatives	0	34
Liability Derivatives	(1)	(2)
Credit derivatives that purchase credit protection \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	61	78
Fair Value	1	(1)
Asset Derivatives	1	0
Liability Derivatives	0	(1)
Credit derivatives that assume credit risk \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	823	851
Fair Value	3	6
Asset Derivatives	20	10
Liability Derivatives	(17)	(4)
Credit derivatives in offsetting positions \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	1,046	2,311
Fair Value	2	0
Asset Derivatives	13	23
Liability Derivatives	(11)	(23)
Equity index options \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	258	5
Fair Value	1	0
Asset Derivatives	1	0
Liability Derivatives	0	0
Contingent capital facility put option \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	0	500
Fair Value	0	1
Asset Derivatives	0	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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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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