Employee Benefit Plans Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit (credit) cost	$ (7)	$ (5)
Qualified Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total other components of net benefit (credit) cost	(18)	(14)
Net periodic defined benefit (credit) cost	(10)	(7)
Qualified Defined Benefit Pension Plan | Component recognized in salaries and benefits expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	7
Qualified Defined Benefit Pension Plan | Component recognized in noninterest expense
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	20	19
Expected return on plan assets	(42)	(41)
Amortization of prior service credit	(5)	(5)
Amortization of net loss	(9)	(13)
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	2
Non-Qualified Defined Benefit Pension Plan | Component recognized in salaries and benefits expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	0
Non-Qualified Defined Benefit Pension Plan | Component recognized in noninterest expense
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 expense
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	1	1
Expected return on plan assets	$ (1)	$ (1)