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
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
Property-liability insurance claims and claims expense
Beginning balance	$ 41,079
Incurred claims and claims expense related to:
Prior years	(1,004)	$ (251)
Claims and claims expense paid related to:
Ending balance	41,320
Property and casualty
Property-liability insurance claims and claims expense
Beginning balance	41,079	41,917
Less: recoverables	7,948	9,739	$ 8,012	$ 8,602
Activity in the reserve for property-liability insurance claims and claims expense:
Net beginning balance	33,067	33,315
Incurred claims and claims expense related to:
Current year	10,189	11,066
Prior years	(1,004)	(251)
Total incurred	9,185	10,815
Claims and claims expense paid related to:
Current year	(3,170)	(4,279)
Prior years	(5,710)	(5,755)
Total paid	(8,880)	(10,034)
Net ending balance	33,372	34,096
Plus: recoverables	7,948	9,739	$ 8,012	$ 8,602
Ending balance	$ 41,320	$ 43,835