Other Intangible Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
Amortized intangible assets, gross carrying amount	$ 653		$ 653		$ 647
Amortized intangible assets, accumulated amortization	271		271		253
Amortized intangible liabilities, gross carrying amount	1,403		1,403		1,403
Amortized intangible liabilities, accumulated amortization	977		977		$ 932
Amortization of Intangible Assets	9	$ 9	18	$ 18
Amortization of Intangible Liabilities	22	$ 24	45	$ 48
Finite-Lived Intangible Assets and Liabilities, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Amortization of intangible assets, Remainder of 2018	17		17
Amortization of intangible liabilities, Remainder of 2018	45		45
Amortization of intangible assets, 2019	33		33
Amortization of intangible liabilities, 2019	27		27
Amortization of intangible assets, 2020	33		33
Amortization of intangible liabilities, 2020	26		26
Amortization of intangible assets, 2021	31		31
Amortization of intangible liabilities, 2021	24		24
Amortization of intangible assets, 2022	31		31
Amortization of intangible liabilities, 2022	$ 23		$ 23