Employee Benefit Plans Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit (credit) cost			$ (14)	$ (14)
Qualified Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total other components of net benefit (credit) cost	$ (14)	$ (14)	(43)	(42)
Net periodic defined benefit (credit) cost	(7)	(7)	(21)	(21)
Qualified Defined Benefit Pension Plan | Component recognized in salaries and benefits expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	7	22	21
Qualified Defined Benefit Pension Plan | Component recognized in noninterest expense
Defined Benefit Plan Disclosure [Line Items]
Interest cost	19	19	56	58
Expected return on plan assets	(41)	(39)	(123)	(118)
Amortization of prior service credit	(5)	(5)	(14)	(14)
Amortization of net loss	13	11	38	32
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	7
Non-Qualified Defined Benefit Pension Plan | Component recognized in salaries and benefits expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	1	1
Non-Qualified Defined Benefit Pension Plan | Component recognized in noninterest expense
Defined Benefit Plan Disclosure [Line Items]
Interest cost	2	2	6	6
Amortization of prior service credit	(1)	(2)	(6)	(6)
Amortization of net loss	2	2	7	6
Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit (credit) cost	0	0	1	0
Postretirement Benefit Plan | Component recognized in noninterest expense
Defined Benefit Plan Disclosure [Line Items]
Interest cost	0	1	1	2
Expected return on plan assets	$ 0	$ (1)	$ (2)	$ (2)