Basis of Presentation Basis of Presentation (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Jun. 01, 2018	Mar. 01, 2018	Dec. 31, 2017
Basis of Presentation [Abstract]
Document Fiscal Year Focus	2019
Cash and Cash Equivalents, at Carrying Value	$ 540	$ 544	$ 615
Program cash	131	147	115
Restricted Cash and Cash Equivalents	5	10
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	676	701	735			$ 901
Net Unrealized Gain Or Loss Of Foreign Currency Transactions On Intercompany Loan Hedges	5	$ 1
Assets Held-for-sale, Not Part of Disposal Group	24		25
Equity Method Investments	0		0	$ 19	$ 20
Equity Securities without Readily Determinable Fair Value, Amount	20		8
Equity Securities without Readily Determinable Fair Value, Upward Price Adjustment, Cumulative Amount	12
Other related Revenue	30
Adjustments related to New Accounting Pronouncements [Line Items]
Operating Lease, Right-of-Use Asset	2,506		0
Accounting Standards Update 2016-02 [Member]
Adjustments related to New Accounting Pronouncements [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			5
Property leases [Member]
Adjustments related to New Accounting Pronouncements [Line Items]
Operating Lease, Right-of-Use Asset	2,506
Property leases [Member] | Accounting Standards Update 2016-02 [Member]
Adjustments related to New Accounting Pronouncements [Line Items]
Operating Lease, Right-of-Use Asset			2,811
Vehicle leases [Member]
Adjustments related to New Accounting Pronouncements [Line Items]
Operating Lease, Right-of-Use Asset	$ 147
Vehicle leases [Member] | Accounting Standards Update 2016-02 [Member]
Adjustments related to New Accounting Pronouncements [Line Items]
Operating Lease, Right-of-Use Asset			$ 183