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, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Allowance for Credit Losses on Finance Receivables and Investments in Operating Leases
Allowance for credit losses at beginning of period				$ 602				$ 597	$ 602	$ 597
Charge-offs									(470)	(464)
Recoveries									95	97
Provision for credit losses	$ 326	$ 128	$ 61	$ 75	$ 106	$ 110	$ 67	$ 89	590	372	$ 401
Allowance for credit losses at end of period	$ 817				$ 602				$ 817	$ 602	$ 597