Basis of Presentation and Significant Accounting Policies (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 01, 2018	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements
Operating expenses (excluding depreciation and amortization expense reflected below)		$ 1,136	$ 1,124
General and administrative expenses (excluding depreciation and amortization expense reflected below)		$ 238	192
Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements
Operating expenses (excluding depreciation and amortization expense reflected below)			7
General and administrative expenses (excluding depreciation and amortization expense reflected below)			$ 2
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements
Reclassification of stranded income tax effects of Tax Reform to retained earnings per ASU 2018-02	$ 91