Intangible Assets (Roll-forward of Goodwill by Business Segment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Balance at beginning of period	$ 15,296	$ 15,271
Foreign exchange revaluation and other	60	25
Balance at end of period	15,400	15,296
North America Commercial P&C Insurance
Goodwill [Roll Forward]
Balance at beginning of period	6,955	6,946
Foreign exchange revaluation and other	17	9
Balance at end of period	6,972	6,955
Segment Insurance North American Personal P&C [Member] [Member]
Goodwill [Roll Forward]
Balance at beginning of period	2,234	2,230
Foreign exchange revaluation and other	6	4
Balance at end of period	2,240	2,234
North America Agricultural Insurance
Goodwill [Roll Forward]
Balance at beginning of period	134	134
Foreign exchange revaluation and other	0	0
Balance at end of period	134	134
Overseas General Insurance
Goodwill [Roll Forward]
Balance at beginning of period	4,785	4,770
Foreign exchange revaluation and other	35	15
Balance at end of period	4,836	4,785
Segment Global Reinsurance [Member]
Goodwill [Roll Forward]
Balance at beginning of period	371	371
Foreign exchange revaluation and other	0	0
Balance at end of period	371	371
Life Insurance
Goodwill [Roll Forward]
Balance at beginning of period	817	820
Foreign exchange revaluation and other	2	(3)
Balance at end of period	847	$ 817
Banchile Seguros de Vida [Member]
Goodwill [Roll Forward]
Goodwill, Acquired During Period	44
Banchile Seguros de Vida [Member] | North America Commercial P&C Insurance
Goodwill [Roll Forward]
Goodwill, Acquired During Period	0
Banchile Seguros de Vida [Member] | Segment Insurance North American Personal P&C [Member] [Member]
Goodwill [Roll Forward]
Goodwill, Acquired During Period	0
Banchile Seguros de Vida [Member] | North America Agricultural Insurance
Goodwill [Roll Forward]
Goodwill, Acquired During Period	0
Banchile Seguros de Vida [Member] | Overseas General Insurance
Goodwill [Roll Forward]
Goodwill, Acquired During Period	16
Banchile Seguros de Vida [Member] | Segment Global Reinsurance [Member]
Goodwill [Roll Forward]
Goodwill, Acquired During Period	0
Banchile Seguros de Vida [Member] | Life Insurance
Goodwill [Roll Forward]
Goodwill, Acquired During Period	$ 28