New Accounting Guidance - Early Adoption (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Net receivables	$ 4,562	$ 4,201	$ 4,133
Other current assets	540	542	224
Other assets	1,535	1,656	1,430
Deferred tax assets	554	552	669
Accounts payable and accrued liabilities	2,343	2,205	2,083
Other liabilities	1,267	1,334	1,311
Other Accumulated Comprehensive Income		(14)	0
Retained earnings	13,812	13,504	$ 13,140
Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Net receivables	4,562	68
Other current assets	540	318
Other assets		226
Deferred tax assets	554	(103)
Accounts payable and accrued liabilities	2,343	122
Other liabilities	1,267	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
Cumulative effect of new accounting principle in period of adoption		$ (14)