Marketable Securities (Schedule of Available-for-sale Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 29	$ 31

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

No definition available.

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