Employee Benefit Plans (Net Periodic Costs (Components of Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Amortization of actuarial gain/(loss)	$ (47)	$ (50)	$ (38)
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	160	102	107
Interest cost	179	186	177
Expected return on plan assets	(285)	(281)	(297)
Amortization of prior service cost/(credit)	(3)	(7)	(9)
Amortization of actuarial losses	43	45	31
Net periodic cost/(benefit)	94	45	9
Current year prior service cost/(credit)	17
Amortization of prior service (cost)/credit	3	7	9
Current year actuarial loss/(gain)	(264)	91	152
Amortization of actuarial gain/(loss)	(43)	(45)	(31)
Total recognized in OCI	(287)	53	130
Total amount recognized in net periodic cost and OCI	(193)	98	139
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	10	12	11
Amortization of actuarial losses	4	5	7
Net periodic cost/(benefit)	17	20	21
Current year actuarial loss/(gain)	7	7	(10)
Amortization of actuarial gain/(loss)	(4)	(5)	(7)
Total recognized in OCI	3	2	(17)
Total amount recognized in net periodic cost and OCI	20	22	4
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	6	5
Interest cost	14	15	15
Expected return on plan assets	(5)	(6)
Amortization of prior service cost/(credit)	(1)	(1)	(1)
Net periodic cost/(benefit)	13	14	19
Current year prior service cost/(credit)	2
Amortization of prior service (cost)/credit	1	1	1
Current year actuarial loss/(gain)	(22)	17	(9)
Total recognized in OCI	(19)	18	(8)
Total amount recognized in net periodic cost and OCI	$ (6)	$ 32	$ 11