Basis of Presentation and Other Information Reclassification of prior period amounts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018	Mar. 31, 2017
Reclassification of prior period amounts [Line Items]
Revenue, equipment rentals, net	$ 1,253	$ 966	$ 2,465	$ 1,865
Depreciation, equipment rentals	1,181	888	2,317	1,742
Proceeds from Sale and Collection of Receivables			223	640
Payments to Acquire Equipment on Lease			3,524	3,065
Net Cash Provided by (Used in) Financing Activities			44	(2,560)
Net Cash Provided by (Used in) Investing Activities			(6,287)	(237)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 5,773	4,871	$ 5,773	4,871	$ 6,659	$ 2,942
Accounting Standards Update 2016-15 [Member]
Reclassification of prior period amounts [Line Items]
Net Cash Provided by (Used in) Financing Activities				129
Net Cash Provided by (Used in) Investing Activities				(2)
Adjustments for New Accounting Pronouncement [Member]
Reclassification of prior period amounts [Line Items]
Payments to Acquire Equipment on Lease				2,000
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents						$ 72
Cost of Equipment Rentals [Member]
Reclassification of prior period amounts [Line Items]
Prior Period Reclassification Adjustment		$ 112		$ 224