Derivative Financial Instruments - Net Gain (Loss) Recognized in Income on Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative [Line Items]
Derivative gain (loss)	$ 73	$ 60	$ 259	$ 154
Futures | Net gain (loss) on mortgage servicing rights
Derivative [Line Items]
Derivative gain (loss)	0	0	1	(2)
Interest rate swaps and swaptions | Net gain (loss) on mortgage servicing rights
Derivative [Line Items]
Derivative gain (loss)	(2)	28	39	71
Mortgage-backed securities forwards | Net gain (loss) on mortgage servicing rights
Derivative [Line Items]
Derivative gain (loss)	5	3	28	23
Rate lock commitments and MSR forwards | Net gain (loss) on loan sales
Derivative [Line Items]
Derivative gain (loss)	70	27	190	57
Forward commitments | Other noninterest income
Derivative [Line Items]
Derivative gain (loss)	0	0	0	2
Interest rate swaps | Other noninterest income
Derivative [Line Items]
Derivative gain (loss)	$ 0	$ 2	$ 1	$ 3