Reserve for Property and Casualty Insurance Claims and Claims Expense - Schedule of Rollforward of the Reserve for Property and Casualty Insurance Claims and Claims Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2023
Property-liability insurance claims and claims expense
Beginning balance	$ 41,917
Incurred claims and claims expense related to:
Prior years	(251)	$ (151)
Claims and claims expense paid related to:
Ending balance	43,835		$ 41,917
Property and casualty
Property-liability insurance claims and claims expense
Beginning balance	41,917	39,858	40,143
Less: recoverables	9,739	8,333	8,602	$ 8,396
Activity in the reserve for property-liability insurance claims and claims expense:
Net beginning balance	33,315	31,462	31,810
Incurred claims and claims expense related to:
Current year	11,066	9,652
Prior years	(251)	(151)
Total incurred	10,815	9,501
Claims and claims expense paid related to:
Current year	(4,279)	(3,163)
Prior years	(5,755)	(5,990)
Total paid	(10,034)	(9,153)
Net ending balance	34,096	31,810	33,315
Plus: recoverables	9,739	8,333	8,602	$ 8,396
Ending balance	$ 43,835	$ 40,143	$ 41,917