Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension settlement costs			$ 44
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 55	$ 42	48
Interest cost on projected benefit obligation	88	80	76
Expected return on plan assets	(129)	(99)	(95)
Amortization of unrecognized loss	29	20	37
Net periodic pension benefit cost	43	43	66
Pension settlement costs			44
Net periodic benefit cost	43	43	110
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	19	11	13
Interest cost on projected benefit obligation	30	22	17
Amortization of prior service cost/(credit)	(5)	(4)	(6)
Amortization of unrecognized loss	8	3	8
Net periodic benefit cost	$ 52	$ 32	$ 32