Accounting Principles and Practices - Schedule of Changes to Balance Sheet for Topic 606 (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Jun. 30, 2017
Assets
Receivables, net	$ 2,992	$ 2,730	$ 2,478
Other current assets	732	587	289
Deferred tax assets	452	261	389
Other non-current assets	404	452	307
Liabilities
Accounts payable and accrued liabilities	1,447	1,969	1,961
Other current liabilities	1,121	883	870
Deferred tax liabilities	294	169	127
Other non-current liabilities	1,088	1,099	1,102
Equity
Total equity	4,618	5,155	4,648	$ 5,553
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	2,335
Other current assets	516
Deferred tax assets	580
Other non-current assets	260
Liabilities
Other current liabilities	1,060
Deferred tax liabilities	223
Other non-current liabilities	1,089
Equity
Total equity	3,860
Accounting Standards Update 2014-09 | Adjustments
Assets
Receivables, net	(657)	252
Other current assets	(216)	298
Deferred tax assets	128	(128)
Other non-current assets	(144)	145
Liabilities
Accounts payable and accrued liabilities		8
Other current liabilities	(61)	13
Deferred tax liabilities	(71)	42
Other non-current liabilities	1	(3)
Equity
Total equity	$ (758)	$ 507