Other Comprehensive Income (Schedule of Changes in Accumulated Other Comprehensive Income by Component) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (67)	$ (145)
Other Comprehensive Income (Loss), before Reclassifications	(36)	11
Amounts reclassified from accumulated other comprehensive income (loss)	40	67
Other comprehensive income	4	78	39
Accumulated Other Comprehensive Income (Loss), Ending Balance	(63)	(67)	(145)
Change in Fair Value of Interest Rate Swaps [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(56)	(116)
Other Comprehensive Income (Loss), before Reclassifications	(26)	(4)
Amounts reclassified from accumulated other comprehensive income (loss)	39	64
Other comprehensive income	13	60
Accumulated Other Comprehensive Income (Loss), Ending Balance	(43)	(56)
Change in Fair Value of Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance		5
Other Comprehensive Income (Loss), before Reclassifications		2
Other comprehensive income		2
Accumulated Other Comprehensive Income (Loss), Ending Balance	7	7
Change in Unrecognized Pension Cost Components [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(18)	(34)
Other Comprehensive Income (Loss), before Reclassifications	(10)	13
Amounts reclassified from accumulated other comprehensive income (loss)	1	3
Other comprehensive income	(9)	16
Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (27)	$ (18)