Commitments and Contingencies - Additional Information (Details) - USD ($)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Commitments And Contingencies [Line Items]
Minimum lease commitments	$ 162,000,000	$ 59,000,000
Indemnification provisions	0	0
Putnam and Gibson Counties [Member] | Performance Guarantee [Member]
Commitments And Contingencies [Line Items]
Guarantees of affiliate pollution control and solid waste disposal bonds	100,000,000	100,000,000
Facility Relocation [Member]
Commitments And Contingencies [Line Items]
Relocation costs for employees and other relocation expenses	114,000,000
Relocation costs for employees and other relocation expenses incurred to date	105,000,000
Relocation costs incurred during the period	$ 43,000,000	43,000,000	$ 15,000,000
TMNA [Member]
Commitments And Contingencies [Line Items]
15-year lease agreement between TMCC and TMNA	15 years
Lease agreement expiration date	Aug. 31, 2032
Total rental expense, including payments to affiliates	$ 30,000,000	27,000,000	$ 25,000,000
TMCC-affiliated companies [Member]
Commitments And Contingencies [Line Items]
Minimum lease commitments	105,000,000	$ 10,000,000
TMCC-affiliated companies [Member] | Putnam and Gibson Counties [Member] | Performance Guarantee [Member]
Commitments And Contingencies [Line Items]
Guarantees of affiliate pollution control and solid waste disposal bonds	100,000,000
TMCC-affiliated companies [Member] | Putnam and Gibson Counties [Member] | Performance Guarantee [Member] | 2028 [Member]
Commitments And Contingencies [Line Items]
Guarantees of affiliate pollution control and solid waste disposal bonds	20,000,000
TMCC-affiliated companies [Member] | Putnam and Gibson Counties [Member] | Performance Guarantee [Member] | 2029 [Member]
Commitments And Contingencies [Line Items]
Guarantees of affiliate pollution control and solid waste disposal bonds	50,000,000
TMCC-affiliated companies [Member] | Putnam and Gibson Counties [Member] | Performance Guarantee [Member] | 2030 [Member]
Commitments And Contingencies [Line Items]
Guarantees of affiliate pollution control and solid waste disposal bonds	10,000,000
TMCC-affiliated companies [Member] | Putnam and Gibson Counties [Member] | Performance Guarantee [Member] | 2031 [Member]
Commitments And Contingencies [Line Items]
Guarantees of affiliate pollution control and solid waste disposal bonds	10,000,000
TMCC-affiliated companies [Member] | Putnam and Gibson Counties [Member] | Performance Guarantee [Member] | 2032 [Member]
Commitments And Contingencies [Line Items]
Guarantees of affiliate pollution control and solid waste disposal bonds	10,000,000
TMCC-affiliated companies [Member] | Putnam and Gibson Counties [Member] | Affiliate Pollution Control and Solid Waste Disposal Bonds [Member]
Commitments And Contingencies [Line Items]
Guarantee Fee	$ 78,000