Cash, Cash Equivalents, and Marketable Securities Other Securities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Investments, All Other Investments [Abstract]
Cost Method Investments	$ 233	$ 250

Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments.

No definition available.

Name:	us-gaap_CostMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant