Employee Benefit Plans Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit credit		$ (25)	$ (29)	$ (18)
Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	[1]	32	31	29
Interest cost		70	80	75
Expected return on plan assets		(171)	(166)	(165)
Amortization of prior service (credit) cost		(19)	(19)	(19)
Amortization of net loss		54	34	51
Total other components of net benefit credit or cost	[2]	(66)	(71)	(58)
Net periodic defined benefit credit		(34)	(40)	(29)
Actual return on plan assets		$ 537	$ 579	$ (167)
Actual rate of return on plan assets, percent		18.72%	24.07%	(6.21%)
Weighted-average assumptions, discount rate, percent		3.43%	4.37%	3.74%
Weighted-average assumptions, expected long-term return on plan assets, percent		6.50%	6.50%	6.50%
Weighted-average assumptions, rate of compensation increase, percent		4.00%	4.00%	3.75%
Non-Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	[1]	$ 1	$ 3	$ 2
Interest cost		8	9	8
Expected return on plan assets		0	0	0
Amortization of prior service (credit) cost		(8)	(8)	(8)
Amortization of net loss		9	7	9
Total other components of net benefit credit or cost	[2]	9	8	9
Net periodic defined benefit credit		$ 10	$ 11	$ 11
Weighted-average assumptions, discount rate, percent		3.43%	4.37%	3.74%
Weighted-average assumptions, rate of compensation increase, percent		4.00%	4.00%	3.75%
Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 0	$ 0
Interest cost		1	2	$ 2
Expected return on plan assets		(2)	(3)	(3)
Amortization of net loss		0	1	1
Net periodic defined benefit credit		(1)	0	0
Actual return on plan assets		$ 3	$ 5	$ (1)
Actual rate of return on plan assets, percent		6.00%	9.14%	(2.05%)
Weighted-average assumptions, discount rate, percent		3.26%	4.26%	3.55%
Weighted-average assumptions, expected long-term return on plan assets, percent		5.00%	5.00%	5.00%
Health care cost trend rate assumed		6.25%	6.50%	6.50%
Rate to which the healthcare cost trend rate is assumed to decline (the ultimate trend rate), percent		4.50%	4.50%	4.50%
Defined Benefit Plan Year That Reaches Ultimate Trend Rate In Current Expense		2027	2027	2027

[1] Included in salaries and benefits expense on the Consolidated Statements of Income.

[2] Included in other noninterest expenses on the Consolidated Statements of Income.