Derivative Financial Instruments - Carrying Value of Hedged Items in Fair Value Hedge (Details) - USD ($) $ in Millions		Mar. 31, 2021		Dec. 31, 2020
Securities available-for-sale [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged items	[1]	$ 7,952		$ 7,966
Active hedged asset adjustments		53		681
Discontinued hedged asset adjustments		703		738
Total hedged asset adjustments		756		1,419
Deposits [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items		3,640	[1]	5,214
Active hedged liability adjustments		140		214
Discontinued hedged liability adjustments		0		0
Total hedged liability adjustments		140		214
Long-term Debt [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items	[1]	3,636		2,227
Active hedged liability adjustments		(40)		242
Discontinued hedged liability adjustments		176		(15)
Total hedged liability adjustments		$ 136		$ 227

[1] The carrying amount of securities AFS represents the amortized cost basis.