Basis of Presentation (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015 USD ($) state	Sep. 30, 2015 USD ($) state
Deferred Finance Costs, Noncurrent, Net [Abstract]
Unamortized debt issuance expense	$ 124	$ 124
Geographic Areas, Revenues from External Customers [Abstract]
Number of states in which entity operates (states) | state	14	14
Change in Accounting Method Accounted for as Change in Estimate | Other Pension Plan, Postretirement or Supplemental Plans
Change in Accounting Estimate [Line Items]
Increase in defined benefit plans net periodic benefit cost (less than for the three month period ended)	$ 1	$ 3
Increase in defined benefit plans net periodic benefit cost (financial effect)		The change in methodology resulted in an increase of less than $1 million and $3 million to our net periodic benefit cost for the three and nine months ended September 30, 2015, respectively.