Accounting Principles and Practices - Schedule of Changes to Balance Sheet for Topic 606 (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017
Assets
Receivables, net	$ 2,656	$ 2,730	$ 2,478
Other current assets	727	587	289
Deferred tax assets	476	261	389
Other non-current assets	434	452	307
Liabilities
Accounts payable and accrued liabilities	1,600	1,969	1,961
Other current liabilities	988	883	870
Deferred tax liabilities	273	169	127
Other non-current liabilities	1,090	1,099	1,102
Equity
Total equity	4,328	5,155	4,648	$ 5,247
Calculated under Revenue Guidance in Effect before Topic 606
Assets
Receivables, net			2,478
Other current assets			289
Deferred tax assets			389
Other non-current assets			307
Liabilities
Accounts payable and accrued liabilities			1,961
Other current liabilities			870
Deferred tax liabilities			127
Other non-current liabilities			1,102
Equity
Total equity			$ 4,648
Accounting Standards Update 2014-09 | Calculated under Revenue Guidance in Effect before Topic 606
Assets
Receivables, net	2,162
Other current assets	500
Deferred tax assets	604
Other non-current assets	284
Liabilities
Other current liabilities	975
Deferred tax liabilities	214
Other non-current liabilities	1,092
Equity
Total equity	3,655
Accounting Standards Update 2014-09 | Adjustments
Assets
Receivables, net	(494)	252
Other current assets	(227)	298
Deferred tax assets	128	(128)
Other non-current assets	(150)	145
Liabilities
Accounts payable and accrued liabilities		8
Other current liabilities	(13)	13
Deferred tax liabilities	(59)	42
Other non-current liabilities	2	(3)
Equity
Total equity	$ (673)	$ 507