Other Comprehensive Income (Schedule of Changes in Accumulated Other Comprehensive Income (Loss) by Component) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (21)	$ (62)
Other comprehensive income (loss) before reclassifications	8	13
Amounts reclassified from accumulated other comprehensive income	9	28
Other comprehensive income	17	41	$ 9
Cumulative Effect of New Accounting Principle in Period of Adoption	(6)
Accumulated Other Comprehensive Income (Loss), Ending Balance	(10)	(21)	(62)
Change in Fair Value of Interest Rate Swaps [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(12)	(31)
Other comprehensive income (loss) before reclassifications	12
Amounts reclassified from accumulated other comprehensive income	8	19
Other comprehensive income	20	19
Cumulative Effect of New Accounting Principle in Period of Adoption	(3)
Accumulated Other Comprehensive Income (Loss), Ending Balance	5	(12)	(31)
Change in Fair Value of Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(2)	(10)
Other comprehensive income (loss) before reclassifications	(2)	8
Amounts reclassified from accumulated other comprehensive income
Other comprehensive income	(2)	8
Cumulative Effect of New Accounting Principle in Period of Adoption	(3)
Accumulated Other Comprehensive Income (Loss), Ending Balance	(7)	(2)	(10)
Change in Unrecognized Pension Cost Components [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(7)	(21)
Other comprehensive income (loss) before reclassifications	(2)	5
Amounts reclassified from accumulated other comprehensive income	1	9
Other comprehensive income	(1)	14
Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (8)	$ (7)	$ (21)