Other Comprehensive Income (Schedule of Changes in Accumulated Other Comprehensive Income by Component) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (70)	$ (58)	$ (63)	$ (67)
Other Comprehensive Income (Loss), before Reclassifications		(9)	(14)	(11)
Amounts reclassified from accumulated other comprehensive income (loss)	6	12	13	23
Other comprehensive income (loss)	6	3	(1)	12
Accumulated Other Comprehensive Income (Loss), Ending Balance	(64)	(55)	(64)	(55)
Change in Fair Value of Interest Rate Swaps [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(52)	(47)	(43)	(56)
Other Comprehensive Income (Loss), before Reclassifications	2	(12)	(13)	(14)
Amounts reclassified from accumulated other comprehensive income (loss)	6	12	12	23
Other comprehensive income (loss)	8		(1)	9
Accumulated Other Comprehensive Income (Loss), Ending Balance	(44)	(47)	(44)	(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	8	7	7	7
Other Comprehensive Income (Loss), before Reclassifications	(2)	3	(1)	3
Other comprehensive income (loss)	(2)	3	(1)	3
Accumulated Other Comprehensive Income (Loss), Ending Balance	6	10	6	10
Change in Unrecognized Pension Cost Components [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(26)	(18)	(27)	(18)
Amounts reclassified from accumulated other comprehensive income (loss)			1
Other comprehensive income (loss)			1
Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (26)	$ (18)	$ (26)	$ (18)