Employee Benefit Plans (Retirement Plan Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plans	$ 57	$ 57	$ 52
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost (benefits earned during the period)	78	82	92
Interest cost	106	113	112
Expected return on plan assets	(145)	(137)	(129)
Settlement charges	0	(5)	60
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment	0	0	0
Amortization of actuarial loss	65	56	69
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(7)	2	2
Net periodic defined benefit plan expense	97	111	206
Pension Expense	154	168	258
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost (benefits earned during the period)	2	3	5
Interest cost	6	8	8
Settlement charges	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment	0	(38)	0
Amortization of actuarial loss	4	3	7
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(13)	(17)	(17)
Net periodic defined benefit plan expense	(1)	(41)	3
Pension Expense	$ (1)	$ (41)	$ 3