Level 4~Derivatives - Derivative Balance Sheet Classification (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Notional Amount	$ 12,875	$ 12,730
Fair Value	(74)	(90)
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	499	469
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	573	559
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	1,702	9,957
Fair Value	12	10
Asset Derivatives	35	448
Liability Derivatives	(23)	(438)
Other liabilities
Derivatives, Fair Value [Line Items]
Notional Amount	11,020	2,620
Fair Value	(86)	(100)
Asset Derivatives	464	21
Liability Derivatives	(550)	(121)
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	10,546	10,387
Fair Value	(54)	(77)
Asset Derivatives	362	375
Liability Derivatives	(416)	(452)
Interest Rate Swap [Member] \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	2,176	2,190
Fair Value	0	0
Asset Derivatives	137	94
Liability Derivatives	(137)	(94)
Interest Rate Swap [Member] \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	7,200	7,300
Foreign currency swaps \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	153	153
Fair Value	(20)	(13)
Asset Derivatives	0	0
Liability Derivatives	(20)	(13)
Cash Flow Hedging
Derivatives, Fair Value [Line Items]
Notional Amount	2,329	2,343
Fair Value	(20)	(13)
Asset Derivatives	137	94
Liability Derivatives	(157)	(107)
Interest rate swaps and futures \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	8,108	7,986
Fair Value	(66)	(83)
Asset Derivatives	338	340
Liability Derivatives	(404)	(423)
Foreign currency swaps and forwards \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	362	213
Fair Value	(1)	(1)
Asset Derivatives	1	0
Liability Derivatives	(2)	(1)
Credit derivatives that purchase credit protection \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	7	61
Fair Value	0	1
Asset Derivatives	0	1
Liability Derivatives	0	0
Credit Default Swap, Selling Protection [Member] \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	978	823
Fair Value	12	3
Asset Derivatives	14	20
Liability Derivatives	(2)	(17)
Credit derivatives in offsetting positions \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	965	1,046
Fair Value	0	2
Asset Derivatives	8	13
Liability Derivatives	(8)	(11)
Equity index options \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional Amount	126	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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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 not subject to a master netting arrangement and elected not to be offset.

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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
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-SubTopic 20
-Section 50
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Fair value, before effects of master netting arrangements, of a financial liability or 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 liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Fair value, before effects of master netting arrangements, of a financial liability or 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 liabilities not subject to a master netting arrangement and elected not to be offset.

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