Employee Benefit Plans Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit (credit) cost	$ (5)	$ (7)
Qualified Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total other components of net benefit (credit) cost	(16)	(18)
Net periodic defined benefit (credit) cost	(8)	(10)
Qualified Defined Benefit Pension Plan | Component recognized in salaries and benefits expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	8
Qualified Defined Benefit Pension Plan | Component recognized in noninterest expenses
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	18	20
Expected return on plan assets	(43)	(42)
Amortization of prior service credit	(5)	(5)
Amortization of net loss	14	9
Non-Qualified Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total other components of net benefit (credit) cost	2	2
Net periodic defined benefit (credit) cost	3	3
Non-Qualified Defined Benefit Pension Plan | Component recognized in salaries and benefits expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Non-Qualified Defined Benefit Pension Plan | Component recognized in noninterest expenses
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	2	2
Amortization of prior service credit	(2)	(2)
Amortization of net loss	2	2
Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit (credit) cost	0	0
Postretirement Benefit Plan | Component recognized in noninterest expenses
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	0	1
Expected return on plan assets	$ 0	$ (1)