Other Comprehensive Income (Schedule of Changes in Accumulated Other Comprehensive Income by Component) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (63)	$ (67)
Other Comprehensive Income (Loss), before Reclassifications	(14)	(2)
Amounts reclassified from accumulated other comprehensive income (loss)	7	11
Other comprehensive (loss) income	(7)	9
Accumulated Other Comprehensive Income (Loss), Ending Balance	(70)	(58)
Change in Fair Value of Interest Rate Swaps [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(43)	(56)
Other Comprehensive Income (Loss), before Reclassifications	(15)	(2)
Amounts reclassified from accumulated other comprehensive income (loss)	6	11
Other comprehensive (loss) income	(9)	9
Accumulated Other Comprehensive Income (Loss), Ending Balance	(52)	(47)
Change in Fair Value of Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	7		7
Other Comprehensive Income (Loss), before Reclassifications	1
Other comprehensive (loss) income	1
Accumulated Other Comprehensive Income (Loss), Ending Balance	8	7	7
Change in Unrecognized Pension Cost Components [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(27)		(18)
Amounts reclassified from accumulated other comprehensive income (loss)	1
Other comprehensive (loss) income	1
Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (26)	$ (18)	$ (18)