Summary of Significant Accounting Policies (Supplemental Disclosure of Cash Flow Information) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of Significant Accounting Policies [Abstract]
Accruals for capital expenditures		$ 412	$ 584	$ 381
Interest	[1]	205	178	184
Income taxes, net of refunds received		567	405	293
Interest costs capitalized		$ 49	$ 36	$ 23

[1] Included in this amount are approximately $49 million, $36 million, and $23 million of interest costs that were capitalized as part of property, plant and equipment, net of accumulated depreciation, in 2018, 2017 and 2016, respectively.