New Accounting Guidance - Early Adoption (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Net receivables	$ 4,476	$ 4,201	$ 4,133
Other current assets	539	542	224
Other assets	1,381	1,656	1,430
Deferred tax assets	497	552	669
Accounts payable and accrued liabilities	2,293	2,205	2,083
Other liabilities	1,322	1,334	1,311
Other Accumulated Comprehensive Income		(14)	0
Retained earnings	14,196	13,504	$ 13,140
Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Net receivables	4,476	68
Other current assets	539	318
Other assets	1,381	226
Deferred tax assets	497	(103)
Accounts payable and accrued liabilities	2,293	122
Other liabilities	1,322	23
Other Accumulated Comprehensive Income		0
Retained earnings	$ 364	364
Accounting Standards Update 2016-01
Disaggregation of Revenue [Line Items]
Net receivables		0
Other current assets		0
Other assets		0
Deferred tax assets		0
Accounts payable and accrued liabilities		0
Other liabilities		0
Other Accumulated Comprehensive Income		(14)
Retained earnings		14
Accounting Standards Update 2016-16
Disaggregation of Revenue [Line Items]
Net receivables		0
Other current assets		0
Other assets		0
Deferred tax assets		(14)
Accounts payable and accrued liabilities		0
Other liabilities		0
Other Accumulated Comprehensive Income		0
Retained earnings		$ (14)