Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Special termination benefits	$ 26
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	88	$ 55	$ 42
Interest cost on projected benefit obligation	122	88	80
Expected return on plan assets	(168)	(129)	(99)
Amortization of unrecognized loss	40	29	20
Net periodic benefit cost	82	43	43
Special termination benefits	23
Total Disclosed Benefit Cost	105	43	43
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	19	19	11
Interest cost on projected benefit obligation	37	30	22
Amortization of prior service cost/(credit)	(9)	(5)	(4)
Amortization of unrecognized loss	1	8	3
Net periodic benefit cost	48	52	32
Special termination benefits	3
Total Disclosed Benefit Cost	$ 51	$ 52	$ 32