Other Comprehensive Income (Schedule of Changes in Accumulated Other Comprehensive Income (Loss) by Component) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive (Loss) Income, Beginning Balance	$ (62)	$ (73)
Other comprehensive (loss) income before reclassifications	3	(26)
Amounts reclassified from accumulated other comprehensive income	5	10
Other comprehensive income (loss)	8	(16)
Accumulated Other Comprehensive (Loss) Income, Ending Balance	(54)	(89)
Change in Fair Value of Interest Rate Swaps [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive (Loss) Income, Beginning Balance	(31)	(48)
Other comprehensive (loss) income before reclassifications		(28)
Amounts reclassified from accumulated other comprehensive income	5	9
Other comprehensive income (loss)	5	(19)
Accumulated Other Comprehensive (Loss) Income, Ending Balance	(26)	(67)
Change in Fair Value of Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive (Loss) Income, Beginning Balance	(10)	1
Other comprehensive (loss) income before reclassifications	3	2
Amounts reclassified from accumulated other comprehensive income
Other comprehensive income (loss)	3	2
Accumulated Other Comprehensive (Loss) Income, Ending Balance	(7)	3
Change in Unrecognized Pension Cost Components [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive (Loss) Income, Beginning Balance	(21)	(26)
Amounts reclassified from accumulated other comprehensive income		1
Other comprehensive income (loss)		1
Accumulated Other Comprehensive (Loss) Income, Ending Balance	$ (21)	$ (25)