Allowance for Credit Losses - Allowance for Credit Losses on Finance Receivables and Investments in Operating Leases (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Allowance for Credit Losses on Finance Receivables and Investments in Operating Leases
Allowance for credit losses at beginning of period				$ 597				$ 622	$ 597	$ 622	$ 535
Charge-offs									(464)	(516)	(574)
Recoveries									97	90	79
Provision for credit losses	$ 106	$ 110	$ 67	$ 89	$ 81	$ 108	$ 127	$ 85	372	401	582
Allowance for credit losses at end of period	$ 602				$ 597				$ 602	$ 597	$ 622