Retirement Plans (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Settlements, Benefit Obligation	$ 255
Defined Benefit Plan, Settlements Benefit obligation threshold	234
Other comprehensive income, Recognition of net actuarial loss for pension settlement costs, before tax	43
Pension and Other Postretirement and Postemployment Benefit Plans, Liabilities	$ 665		$ 699
Defined Benefit Plan, Funded Percentage	80.00%
Capitalization of pension and OPEB expense related to engineering and plant construction	$ 7	$ 6
Additional contributions to pension plan	6
Plan assets receivable	7
Plan assets	2,608		$ 2,766
Defined Benefit Plan, Fair Value of Plan Assets, Period Increase (Decrease)	$ 158
Percentage of increase in pension plan	6.00%
Positive investment returns	$ 98
Benefit payments	$ 269