Retirement Plans (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Capitalization of pension and OPEB expense related to engineering and plant construction		$ 12	$ 10
Defined benefit plan, cash contributions by employer		10
Plan assets	$ 2,628	2,628		$ 1,572
Defined Benefit Plan, Fair Value of Plan Assets, Period Increase (Decrease)		$ 1,056
Percentage of increase in pension plan		67.00%
Positive investment returns		$ 138
Benefit payments		60
Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year		10
Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year		15
Verizon Transaction [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan assets related to acquisition		968
Plan assets, excluding receivable		868
Plan assets receivable	$ 100	100
Percent of assets transferred	90.00%
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, cash contributions by employer		$ 10