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, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Allowance for Credit Losses on Finance Receivables and Investments in Operating Leases
Allowance for credit losses at beginning of period					$ 622				$ 535	$ 622	$ 535	$ 485
Provision for credit losses		$ 81	$ 108	$ 127	$ 85	$ 186	$ 183	$ 161	$ 52	401	582	441
Transferred to held-for-sale	[1]									0	0	(7)
Charge-offs, net of recoveries										(426)	(495)	(384)
Allowance for credit losses at end of period		$ 597				$ 622				$ 597	$ 622	$ 535

[1] Amount relates to the commercial finance business which was sold in fiscal 2016.