Derivative Financial Instruments - Carrying Value of Hedged Items in Fair Value Hedge (Details) - USD ($) $ in Millions		Sep. 30, 2021		Dec. 31, 2020
Securities available-for-sale [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged items	[1]	$ 7,871		$ 7,966
Active hedged asset adjustments		(92)		681
Discontinued hedged asset adjustments		1,033		738
Total hedged asset adjustments		941		1,419
Deposits [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items		1,621	[1]	5,214
Active hedged liability adjustments		(11)		214
Discontinued hedged liability adjustments		132		0
Total hedged liability adjustments		121		214
Long-term Debt [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged liability items	[1]	5,646		2,227
Active hedged liability adjustments		(12)		242
Discontinued hedged liability adjustments		158		(15)
Total hedged liability adjustments		$ 146		$ 227

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