Employee Benefit Plans Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit (credit) cost			$ (14)	$ (10)
Qualified Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total other components of net benefit (credit) cost	$ (17)	$ (15)	(35)	(29)
Net periodic defined benefit (credit) cost	(10)	(7)	(20)	(14)
Qualified Defined Benefit Pension Plan | Component recognized in salaries and benefits expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	8	15	15
Qualified Defined Benefit Pension Plan | Component recognized in noninterest expense
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	20	18	40	37
Expected return on plan assets	(41)	(41)	(83)	(82)
Amortization of prior service credit	(4)	(4)	(9)	(9)
Amortization of net loss	8	12	17	25
Non-Qualified Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total other components of net benefit (credit) cost	2	2	4	4
Net periodic defined benefit (credit) cost	3	3	6	5
Non-Qualified Defined Benefit Pension Plan | Component recognized in salaries and benefits expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	2	1
Non-Qualified Defined Benefit Pension Plan | Component recognized in noninterest expense
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	2	2	4	4
Amortization of prior service credit	(2)	(3)	(4)	(5)
Amortization of net loss	(2)	(3)	(4)	(5)
Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit (credit) cost	0	1	0	1
Postretirement Benefit Plan | Component recognized in noninterest expense
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	0	0	1	1
Expected return on plan assets	$ 0	$ (1)	$ (1)	$ (2)