Leases (Effect Of The Adoption Of ASC 842) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other assets	$ 471		$ 470	$ 265
Other current liabilities	421		426	394
Other liabilities	426		439	281
Deferred income taxes	1,132		1,113	1,109
Accumulated deficit	(2,749)		(2,741)	(2,752)
Operating lease liabilities	208
Operating right-of-use assets	203
Income tax expense	18	$ 13
Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other assets				265
Other current liabilities				394
Other liabilities				281
Deferred income taxes				1,109
Accumulated deficit				$ (2,752)
Other Current Liabilities [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Current operating lease liabilities	45
Other Noncurrent Liabilities [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Noncurrent operating lease liabilities	163
Accounting Standards Update 2016-02 [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other assets			205
Other current liabilities			32
Other liabilities			158
Deferred income taxes			4
Accumulated deficit			$ 11
Operating Lease, Liability, Statement of Financial Position [Extensible List]			us-gaap:OtherLiabilitiesCurrent us-gaap:OtherLiabilitiesNoncurrent
Operating right-of-use assets	$ 205
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent
Current operating lease liabilities			$ 46
Noncurrent operating lease liabilities			168
Accounting Standards Update 2016-02 [Member] | Accumulated Deficit [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Deferred gain on sale of property			15
Tax effect on the gain of sale of property			4
Accounting Standards Update 2016-02 [Member] | Other Current Liabilities [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Deferred gain on sale of property			14
Accounting Standards Update 2016-02 [Member] | Other Noncurrent Liabilities [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Deferred rent			9
Deferred gain on sale of property			1
Accounting Standards Update 2016-02 [Member] | Deferred Tax Liabilities Noncurrent [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Deferred gain on sale of property			$ 15