Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income Reclassification Adjustments (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) Reclassification Adjustments (Parantheticals) [Abstract]
Net holding gain (loss) on investment securities arising during the period, tax (expense) benefit	$ 213	$ (98)
Reclassification adjustment for net realized loss (gain) on investment securities, tax (benefit) expense	(7)	(2)
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, Net of Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities	9	0
Cash flow hedges, holding gain (loss), tax (expense) benefit	(1)	0
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, tax expense	(3)	(1)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	0	0
Net gain (loss) recognized in other comprehensive income, tax (expense) benefit	$ 211	$ (101)

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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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 after tax of other than temporary impairment (OTTI) loss on investment in available-for-sale debt security, recognized in other comprehensive loss.

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