Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Mar. 31, 2024
Segment Reporting Information [Line Items]
Total financing revenues	$ 3,368	$ 3,098	$ 9,874	$ 8,988
Depreciation on operating leases	1,012	1,044	3,061	3,117
Interest expense	1,414	1,230	4,441	3,401
Net financing revenues	942	824	2,372	2,470
Voluntary protection contract revenues and insurance earned premiums	303	282	898	831
Investment and other income (loss), net	111	495	722	639
Net financing revenues and other revenues	1,356	1,601	3,992	3,940
Expenses:
Provision for credit losses	181	206	576	592
Operating and administrative	451	517	1,344	1,414
Voluntary protection contract expenses and insurance losses	159	143	479	434
Total expenses	791	866	2,399	2,440
Income (loss) before income taxes	565	735	1,593	1,500
Provision (benefit) for income taxes	136	174	378	369
Net Income (Loss)	429	561	1,215	1,131
Total assets	154,057	146,683	154,057	146,683	$ 149,381
Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Total financing revenues	0	0	0	0
Depreciation on operating leases	0	0	0	0
Interest expense	0	0	0	0
Net financing revenues	0	0	0	0
Voluntary protection contract revenues and insurance earned premiums	0	0	0	0
Investment and other income (loss), net	0	0	0	0
Net financing revenues and other revenues	0	0	0	0
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative	0	0	0	0
Voluntary protection contract expenses and insurance losses	0	0	0	0
Total expenses	0	0	0	0
Income (loss) before income taxes	0	0	0	0
Provision (benefit) for income taxes	0	0	0	0
Net Income (Loss)	0	0	0	0
Total assets	(86)	(58)	(86)	(58)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	3,368	3,098	9,874	8,988
Depreciation on operating leases	1,012	1,044	3,061	3,117
Interest expense	1,414	1,230	4,441	3,401
Net financing revenues	942	824	2,372	2,470
Voluntary protection contract revenues and insurance earned premiums	0	0	0	0
Investment and other income (loss), net	183	142	485	375
Net financing revenues and other revenues	1,125	966	2,857	2,845
Expenses:
Provision for credit losses	181	206	576	592
Operating and administrative	335	407	994	1,073
Voluntary protection contract expenses and insurance losses	0	0	0	0
Total expenses	516	613	1,570	1,665
Income (loss) before income taxes	609	353	1,287	1,180
Provision (benefit) for income taxes	147	94	308	296
Net Income (Loss)	462	259	979	884
Total assets	146,113	139,440	146,113	139,440
Voluntary Protection Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	0	0	0	0
Depreciation on operating leases	0	0	0	0
Interest expense	0	0	0	0
Net financing revenues	0	0	0	0
Voluntary protection contract revenues and insurance earned premiums	303	282	898	831
Investment and other income (loss), net	(72)	353	237	264
Net financing revenues and other revenues	231	635	1,135	1,095
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative	116	110	350	341
Voluntary protection contract expenses and insurance losses	159	143	479	434
Total expenses	275	253	829	775
Income (loss) before income taxes	(44)	382	306	320
Provision (benefit) for income taxes	(11)	80	70	73
Net Income (Loss)	(33)	302	236	247
Total assets	$ 8,030	$ 7,301	$ 8,030	$ 7,301