Derivative Instruments - Derivatives - Derivative Balance Sheet Classification (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	$ 11,729	$ 12,129
Fair Value	(33)	(61)
Asset Derivatives	33	33
Liability Derivatives	(66)	(94)
Other investments
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	9,657	9,585
Fair Value	22	23
Asset Derivatives	24	25
Liability Derivatives	(2)	(2)
Other liabilities
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,803	2,275
Fair Value	(55)	(84)
Asset Derivatives	9	8
Liability Derivatives	(64)	(92)
Available-for-sale Securities [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	269	269
Fair Value	0	0
Asset Derivatives	0	0
Liability Derivatives	0	0
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	9,092	9,503
Fair Value	(23)	(48)
Asset Derivatives	30	30
Liability Derivatives	(53)	(78)
Interest rate swaps \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	2,340	2,340
Fair Value	0	0
Asset Derivatives	0	0
Liability Derivatives	0	0
Interest rate swaps \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	7,600	7,600
Foreign currency swaps \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	297	286
Fair Value	(10)	(13)
Asset Derivatives	3	3
Liability Derivatives	(13)	(16)
Total cash flow hedges
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	2,637	2,626
Fair Value	(10)	(13)
Asset Derivatives	3	3
Liability Derivatives	(13)	(16)
Interest rate swaps and futures \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	7,926	8,335
Fair Value	(44)	(69)
Asset Derivatives	4	4
Liability Derivatives	(48)	(73)
Foreign currency swaps and forwards \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	269	269
Fair Value	0	0
Asset Derivatives	0	0
Liability Derivatives	0	0
Credit derivatives that purchase credit protection \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	6	6
Fair Value	0	0
Asset Derivatives	0	0
Liability Derivatives	0	0
Credit derivatives that assume credit risk \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	675	675
Fair Value	21	21
Asset Derivatives	21	21
Liability Derivatives	0	0
Credit derivatives in offsetting positions \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	216	218
Fair Value	0	0
Asset Derivatives	5	5
Liability Derivatives	$ (5)	$ (5)

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.

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

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Nominal or face amount used to calculate payment on derivative.

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