Employee Benefit Plans (Net Periodic Costs (Components of Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Amortization of actuarial gain/(loss)	$ (5)	$ (47)	$ (50)
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	116	160	102
Interest cost	171	179	186
Expected return on plan assets	(306)	(285)	(281)
Amortization of prior service cost/(credit)	1	(3)	(7)
Amortization of actuarial (gain)/loss		43	45
Net periodic cost/(benefit)	(18)	94	45
Current year prior service cost/(credit)		17
Amortization of prior service (cost)/credit	(1)	3	7
Current year actuarial loss/(gain)	75	(264)	91
Amortization of actuarial gain/(loss)		(43)	(45)
Total recognized in OCI	74	(287)	53
Total amount recognized in net periodic cost and OCI	56	(193)	98
Additional service cost due to the special, one-time cash balance credit		57
Nonqualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	3
Interest cost	9	10	12
Amortization of actuarial (gain)/loss	5	4	5
Net periodic cost/(benefit)	17	17	20
Current year actuarial loss/(gain)	(16)	7	7
Amortization of actuarial gain/(loss)	(5)	(4)	(5)
Total recognized in OCI	(21)	3	2
Total amount recognized in net periodic cost and OCI	(4)	20	22
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	5	6
Interest cost	12	14	15
Expected return on plan assets	(6)	(5)	(6)
Amortization of prior service cost/(credit)		(1)	(1)
Net periodic cost/(benefit)	11	13	14
Current year prior service cost/(credit)		2
Amortization of prior service (cost)/credit		1	1
Current year actuarial loss/(gain)	(25)	(22)	17
Total recognized in OCI	(25)	(19)	18
Total amount recognized in net periodic cost and OCI	$ (14)	$ (6)	$ 32