Employee Benefit Plans Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit (credit) cost	$ (9)	$ (4)	$ (23)	$ (14)
Qualified Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total other components of net benefit (credit) cost	(18)	(14)	(53)	(43)
Net periodic defined benefit (credit) cost	(10)	(7)	(30)	(21)
Qualified Defined Benefit Pension Plan | Component recognized in salaries and benefits expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	7	23	22
Qualified Defined Benefit Pension Plan | Component recognized in noninterest expense
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	20	19	60	56
Expected return on plan assets	(41)	(41)	(124)	(123)
Amortization of prior service credit	(5)	(5)	(14)	(14)
Amortization of net loss	8	13	25	38
Non-Qualified Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total other components of net benefit (credit) cost	2	3	6	7
Net periodic defined benefit (credit) cost	2	3	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	2	1
Non-Qualified Defined Benefit Pension Plan | Component recognized in noninterest expense
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	3	2	7	6
Amortization of prior service credit	(2)	(1)	(6)	(6)
Amortization of net loss	1	2	5	7
Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit (credit) cost	(1)	0	(1)	(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	$ (1)	$ 0	$ (2)	$ (2)