Accounting Principles and Practices - Schedule of Changes to Balance Sheet for Topic 606 (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
ASSETS
Receivables, net	$ 3,053	$ 2,730	$ 2,478
Other current assets	609	587	289
Deferred tax assets	296	261	389
LIABILITIES
Other non-current assets	439	452	307
Accounts payable and accrued liabilities	1,545	1,969	1,961
Other current liabilities	972	883	870
Deferred tax liabilities	243	169	127
Other non-current liabilities	1,105	1,099	1,102
EQUITY
Total equity	5,385	5,155	4,648	$ 5,826	$ 5,532
Calculated under Revenue Guidance in Effect before Topic 606
ASSETS
Receivables, net			2,478
Other current assets			289
Deferred tax assets			389
LIABILITIES
Other non-current assets			307
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	2,409
Other current assets	370
Deferred tax assets	426
LIABILITIES
Other non-current assets	296
Other current liabilities	920
Deferred tax liabilities	175
Other non-current liabilities	1,108
EQUITY
Total equity	4,606
Accounting Standards Update 2014-09 | Adjustments
ASSETS
Receivables, net	(644)	252
Other current assets	(239)	298
Deferred tax assets	130	(128)
LIABILITIES
Other non-current assets	(143)	145
Accounts payable and accrued liabilities		8
Other current liabilities	(52)	13
Deferred tax liabilities	(68)	42
Other non-current liabilities	3	(3)
EQUITY
Total equity	$ (779)	$ 507