Basis of Presentation and Significant Accounting Policies (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basis of Presentation and Significant Accounting Policies (Textual)
Operating expenses (excluding depreciation and amortization expense)		$ 1,193	$ 1,135	$ 3,439	$ 3,370
General and administrative expenses (excluding depreciation and amortization expense)		$ 209	225	695	592
Reclassification of stranded income tax effects of Tax Reform to retained earnings per ASU 2018-02				$ 0
Accounting Standards Update 2017-07 [Member]
Basis of Presentation and Significant Accounting Policies (Textual)
Operating expenses (excluding depreciation and amortization expense)			10		31
General and administrative expenses (excluding depreciation and amortization expense)			$ (4)		$ (5)
Accounting Standards Update 2018-02 [Member]
Basis of Presentation and Significant Accounting Policies (Textual)
Reclassification of stranded income tax effects of Tax Reform to retained earnings per ASU 2018-02	$ 91
Minimum [Member]
Basis of Presentation and Significant Accounting Policies (Textual)
Typical post-delivery payment terms (in days)				2 days
Maximum [Member]
Basis of Presentation and Significant Accounting Policies (Textual)
Typical post-delivery payment terms (in days)				10 days