Basis of Presentation and Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022	Apr. 01, 2023	Apr. 01, 2022
Summary Of Significant Accounting Policies [Line Items]
Decrease to depreciation on operating leases	$ (1,062)	$ (1,044)	$ (918)	$ (1,155)		$ (4,179)	$ (5,122)	$ (5,846)
Net income						$ 1,460	$ 979	$ 2,535
Effective tax rate						23.20%	25.20%	23.70%
Retained earnings	16,130					$ 16,130	$ 15,649
Allowance for credit losses	$ 1,637					1,637	$ 1,489
ASU 2021-05 [Member]
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adoption date										Apr. 01, 2022
Change in accounting principle, accounting standards update, adopted [true false]										true
Change in accounting principle, accounting standards update, immaterial effect [true false]										true
ASU 2022-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adoption date									Apr. 01, 2023
Change in accounting principle, accounting standards update, adopted [true false]									true
Change in accounting principle, accounting standards update, immaterial effect [true false]									true
Revision of Prior Period, Change in Accounting Principle, Adjustment [Member]
Summary Of Significant Accounting Policies [Line Items]
Decrease to depreciation on operating leases						60
Increase to our provision for income taxes						205
Net income						$ 145
Effective tax rate					10.50%	23.20%
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | Finance Operations [Member] | California [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration Percentage						21.00%
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | Finance Operations [Member] | Texas [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration Percentage						13.00%
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | Finance Operations [Member] | New York [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration Percentage						7.00%
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | Finance Operations [Member] | New Jersey [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration Percentage						5.00%
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | Voluntary Protection Operations [Member] | California [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration Percentage						23.00%
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | Voluntary Protection Operations [Member] | New York [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration Percentage						6.00%
Geographic Concentration Risk [Member] | Sales Revenue, Net [Member] | Voluntary Protection Operations [Member] | Maryland [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration Percentage						5.00%