Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Notional Amount of Derivatives	$ 19,446	$ 19,885
Derivative Asset, Fair Value, Gross Asset	258	357
Derivative Liability, Fair Value, Gross Liability	1,003	990
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount of Derivatives	17,475	18,044
Derivative Asset, Fair Value, Gross Asset	212	255
Derivative Liability, Fair Value, Gross Liability	970	963
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Notional Amount of Derivatives	909	1,041
Derivative Asset, Fair Value, Gross Asset	70	47
Derivative Liability, Fair Value, Gross Liability	3	1
Not Designated as Hedging Instrument [Member] | Future [Member]
Derivative [Line Items]
Notional Amount of Derivatives	307	326
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	0	0
Not Designated as Hedging Instrument [Member] | Foreign Exchange Forward [Member]
Derivative [Line Items]
Notional Amount of Derivatives	175	25
Derivative Asset, Fair Value, Gross Asset	1	0
Derivative Liability, Fair Value, Gross Liability	0	0
Not Designated as Hedging Instrument [Member] | Consumer Price Index Swap [Member]
Derivative [Line Items]
Notional Amount of Derivatives	441	386
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	28	11
Not Designated as Hedging Instrument [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Notional Amount of Derivatives	1,306	1,338
Derivative Asset, Fair Value, Gross Asset	5	6
Derivative Liability, Fair Value, Gross Liability	0	1
Not Designated as Hedging Instrument [Member] | Equity [Member]
Derivative [Line Items]
Notional Amount of Derivatives	364	439
Derivative Asset, Fair Value, Gross Asset	15	43
Derivative Liability, Fair Value, Gross Liability	0	0
Not Designated as Hedging Instrument [Member] | Longevity Swap [Member]
Derivative [Line Items]
Notional Amount of Derivatives	0	917
Derivative Asset, Fair Value, Gross Asset	0	48
Derivative Liability, Fair Value, Gross Liability	0	0
Not Designated as Hedging Instrument [Member] | Mortality Swap [Member]
Derivative [Line Items]
Notional Amount of Derivatives	0	25
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	0	0
Not Designated as Hedging Instrument [Member] | Synthetic Guaranteed Investment Contracts [Member]
Derivative [Line Items]
Notional Amount of Derivatives	13,823	13,397
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	0	0
Not Designated as Hedging Instrument [Member] | Embedded Derivatives In Modified Coinsurance Or Funds Withheld Arrangements [Member]
Derivative [Line Items]
Notional Amount of Derivatives	0	0
Derivative Asset, Fair Value, Gross Asset	121	110
Derivative Liability, Fair Value, Gross Liability	0	0
Not Designated as Hedging Instrument [Member] | Embedded Derivatives In Indexed Annuity [Member]
Derivative [Line Items]
Notional Amount of Derivatives	0	0
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	767	777
Not Designated as Hedging Instrument [Member] | Embedded Derivatives In Variable Annuity [Member]
Derivative [Line Items]
Notional Amount of Derivatives	0	0
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Gross Liability	163	168
Not Designated as Hedging Instrument [Member] | Currency Swap [Member]
Derivative [Line Items]
Notional Amount of Derivatives	150	150
Derivative Asset, Fair Value, Gross Asset	0	1
Derivative Liability, Fair Value, Gross Liability	9	5
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount of Derivatives	1,971	1,841
Derivative Asset, Fair Value, Gross Asset	46	102
Derivative Liability, Fair Value, Gross Liability	33	27
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Notional Amount of Derivatives	535	435
Derivative Asset, Fair Value, Gross Asset	1	0
Derivative Liability, Fair Value, Gross Liability	29	27
Designated as Hedging Instrument [Member] | Foreign Exchange Forward [Member]
Derivative [Line Items]
Notional Amount of Derivatives	1,094	911
Derivative Asset, Fair Value, Gross Asset	28	51
Derivative Liability, Fair Value, Gross Liability	2	0
Designated as Hedging Instrument [Member] | Currency Swap [Member]
Derivative [Line Items]
Notional Amount of Derivatives	342	495
Derivative Asset, Fair Value, Gross Asset	17	51
Derivative Liability, Fair Value, Gross Liability	$ 2	$ 0