Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017
Commitments And Contingencies [Line Items]
Minimum lease commitments		$ 173,000,000		$ 173,000,000		$ 59,000,000
Indemnification provisions		0		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		100,000,000
Facility Relocation [Member]
Commitments And Contingencies [Line Items]
Relocation costs for employees and other relocation expenses		120,000,000		120,000,000
Relocation costs for employees and other relocation expenses incurred to date		96,000,000		96,000,000
Relocation costs incurred during the period		23,000,000	$ 11,000,000	34,000,000	$ 17,000,000
TMNA [Member]
Commitments And Contingencies [Line Items]
15-year lease agreement between TMCC and TMNA	15 years
Lease agreement expiration date	Aug. 31, 2032
TMCC-affiliated companies [Member]
Commitments And Contingencies [Line Items]
Minimum lease commitments		114,000,000		114,000,000		$ 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		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		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		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		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		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		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]
Guaranty Fee				$ 78,000