Goodwill (Roll-forward of Goodwill by Business Segment) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2025 USD ($)
Goodwill [Roll Forward]
Balance at beginning of period	$ 19,579
Foreign exchange revaluation	422
Balance at end of period	20,184	[1]
goodwill attributable to noncontrolling interests	456
North America Commercial P&C Insurance [Member]
Goodwill [Roll Forward]
Balance at beginning of period	7,168
Foreign exchange revaluation	28
Balance at end of period	7,196	[1]
North American Personal P&C Insurance [Member]
Goodwill [Roll Forward]
Balance at beginning of period	2,218
Foreign exchange revaluation	10
Balance at end of period	2,228	[1]
North America Agricultural Insurance [Member]
Goodwill [Roll Forward]
Balance at beginning of period	134
Foreign exchange revaluation	0
Balance at end of period	134	[1]
Overseas General Insurance [Member]
Goodwill [Roll Forward]
Balance at beginning of period	5,047
Foreign exchange revaluation	256
Balance at end of period	5,486	[1]
Global Reinsurance [Member]
Goodwill [Roll Forward]
Balance at beginning of period	371
Foreign exchange revaluation	0
Balance at end of period	371	[1]
Segment Life [Member]
Goodwill [Roll Forward]
Balance at beginning of period	4,641
Foreign exchange revaluation	128
Balance at end of period	4,769	[1]
LMG Insurance, Thailand [Member]
Goodwill [Roll Forward]
Acquisition of Liberty Mutual's P&C insurance business in Thailand	183
LMG Insurance, Thailand [Member] | North America Commercial P&C Insurance [Member]
Goodwill [Roll Forward]
Acquisition of Liberty Mutual's P&C insurance business in Thailand	0
LMG Insurance, Thailand [Member] | North American Personal P&C Insurance [Member]
Goodwill [Roll Forward]
Acquisition of Liberty Mutual's P&C insurance business in Thailand	0
LMG Insurance, Thailand [Member] | North America Agricultural Insurance [Member]
Goodwill [Roll Forward]
Acquisition of Liberty Mutual's P&C insurance business in Thailand	0
LMG Insurance, Thailand [Member] | Overseas General Insurance [Member]
Goodwill [Roll Forward]
Acquisition of Liberty Mutual's P&C insurance business in Thailand	183
LMG Insurance, Thailand [Member] | Global Reinsurance [Member]
Goodwill [Roll Forward]
Acquisition of Liberty Mutual's P&C insurance business in Thailand	0
LMG Insurance, Thailand [Member] | Segment Life [Member]
Goodwill [Roll Forward]
Acquisition of Liberty Mutual's P&C insurance business in Thailand	$ 0

[1] Includes $456 million attributable to noncontrolling interests.