Retirement Plans and Other Benefits - Narrative (Details) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended			9 Months Ended	7 Months Ended	9 Months Ended		9 Months Ended
	Jul. 31, 2012	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 Other Benefits Age	Jul. 31, 2014 Pension Benefits	Sep. 30, 2014 Pension Benefits	Dec. 31, 2014 Expected contributions Other Benefits	Sep. 30, 2014 Maximum Pension Benefits
Regulatory Assets
Regulatory asset amortization period	3 years
Amortization of regulatory asset		$ 2,000,000	$ 2,000,000	$ 6,000,000	$ 6,000,000
Other Postretirement Benefit Plan Remeasurement
Age eligible for benefit							65
Effect on net periodic benefit cost										10,000,000
Decrease (increase) of expenses										5,000,000
Effect on accumulated benefit obligation							316,000,000
Defined benefit plan, assets for plan benefits, noncurrent		180,527,000		180,527,000		0	181,000,000
Other postretirement plan benefit remeasurement, regulatory liabilities							254,000,000
Other postretirement plan benefit remeasurement, amount seeking approval to move to separate account to Pay Union employee medical costs							100,000,000
Contributions
Voluntary employer contributions to pension plan								175,000,000
Minimum employer contributions for the next three years									141,000,000
Defined Benefit Plans Estimated Minimum Future Employer Contributions [Abstract]
2014									0
2015									19,000,000
2016									122,000,000
Maximum future employer contributions in 2015											100,000,000
Maximum future employer contributions in 2016											$ 25,000,000