Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit (credit) cost			$ (19)	$ (23)
Qualified Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total other components of net benefit (credit) cost	$ 17	$ (18)	50	(53)
Net periodic defined benefit (credit) cost	(9)	(10)	(26)	(30)
Qualified Defined Benefit Pension Plan | Component recognized in salaries and benefits expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	8	24	23
Qualified Defined Benefit Pension Plan | Component recognized in noninterest expenses
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	18	20	53	60
Expected return on plan assets	(43)	(41)	(128)	(124)
Amortization of prior service credit	(5)	(5)	(15)	(14)
Defined Benefit Plan, Amortization of Gain (Loss)	13	8	40	25
Non-Qualified Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total other components of net benefit (credit) cost	3	2	7	6
Net periodic defined benefit (credit) cost	3	2	8	8
Non-Qualified Defined Benefit Pension Plan | Component recognized in salaries and benefits expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	1	2
Non-Qualified Defined Benefit Pension Plan | Component recognized in noninterest expenses
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	2	3	6	7
Amortization of prior service credit	(2)	(2)	(6)	(6)
Defined Benefit Plan, Amortization of Gain (Loss)	3	1	7	5
Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit (credit) cost	0	(1)	(1)	(1)
Postretirement Benefit Plan | Component recognized in noninterest expenses
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	1	0	1	1
Expected return on plan assets	$ (1)	$ (1)	$ (2)	$ (2)