Accumulated Other Comprehensive Income (Other Comprehensive Income (Loss) Reclassification Adjustments) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) Reclassification Adjustments (Parantheticals) [Abstract]
Net holding gain (loss) on investment securities arising during the period, tax (expense) benefit	$ (198)	$ 133	$ (153)
Reclassification adjustment for net realized loss (gain) on investment securities, tax (benefit) expense	4	(13)	58
Non-credit component of other-than-temporary impairments on investments, tax (expense) benefit	0	1	(3)
Cash flow hedges, holding gain (loss), tax (expense) benefit	4	(10)	35
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, tax (expense) benefit	(9)	29	(35)
Foreign currency translation adjustment, tax (expense) benefit	0	0	(1)
Net gain (loss) realized in other comprehensive loss, tax (expense) benefit	$ (199)	$ 140	$ (99)

Accumulated Other Comprehensive Income (Loss) Reclassification Adjustments (Parantheticals) [Abstract]

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Amount of tax expense (benefit), after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of tax expense (benefit), after reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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Amount of tax expense (benefit) allocated to other comprehensive income (loss).

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Amount of tax expense (benefit), before reclassification adjustments, related to increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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Amount of tax (expense) benefit of other than temporary impairment (OTTI) on investment in available-for-sale debt security, recognized in other comprehensive loss, attributable to the parent entity.

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