Intangible Assets (Roll-forward of Goodwill, by Business Segment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Roll Forward]
Balance at beginning of period	$ 4,904	$ 4,603
Purchase price allocation adjustment	(4)	4
Foreign exchange revaluation and other	(300)	(198)
Balance at end of period	4,796	4,904
Insurance - North American P&C
Goodwill [Roll Forward]
Balance at beginning of period	1,211	1,215
Purchase price allocation adjustment	0
Acquisition		0
Foreign exchange revaluation and other	(8)	(4)
Balance at end of period	1,399	1,211
Insurance - North American Agriculture
Goodwill [Roll Forward]
Balance at beginning of period	134	134
Purchase price allocation adjustment	0
Acquisition		0
Foreign exchange revaluation and other	0	0
Balance at end of period	134	134
Insurance - Overseas General
Goodwill [Roll Forward]
Balance at beginning of period	2,366	2,054
Purchase price allocation adjustment	(4)
Acquisition		449
Foreign exchange revaluation and other	(284)	(187)
Balance at end of period	2,078	2,366
Global Reinsurance
Goodwill [Roll Forward]
Balance at beginning of period	365	365
Purchase price allocation adjustment	0
Acquisition		0
Foreign exchange revaluation and other	0	0
Balance at end of period	365	365
Life
Goodwill [Roll Forward]
Balance at beginning of period	828	835
Purchase price allocation adjustment	0
Acquisition		0
Foreign exchange revaluation and other	(8)	(7)
Balance at end of period	820	828
Fianzas Monterrey
Goodwill [Roll Forward]
Acquisition		46
Fianzas Monterrey | Insurance - North American P&C
Goodwill [Roll Forward]
Acquisition		0
Fianzas Monterrey | Insurance - North American Agriculture
Goodwill [Roll Forward]
Acquisition		0
Fianzas Monterrey | Insurance - Overseas General
Goodwill [Roll Forward]
Acquisition		4
Fianzas Monterrey | Global Reinsurance
Goodwill [Roll Forward]
Acquisition		0
Fianzas Monterrey | Life
Goodwill [Roll Forward]
Acquisition		0
ABA Seguros
Goodwill [Roll Forward]
Acquisition		449
ABA Seguros | Insurance - North American P&C
Goodwill [Roll Forward]
Acquisition		0
ABA Seguros | Insurance - North American Agriculture
Goodwill [Roll Forward]
Acquisition		0
ABA Seguros | Insurance - Overseas General
Goodwill [Roll Forward]
Acquisition		46
ABA Seguros | Global Reinsurance
Goodwill [Roll Forward]
Acquisition		0
ABA Seguros | Life
Goodwill [Roll Forward]
Acquisition		$ 0
The Siam Commercial Samaggi Insurance PCL [Member]
Goodwill [Roll Forward]
Acquisition	196
The Siam Commercial Samaggi Insurance PCL [Member] | Insurance - North American P&C
Goodwill [Roll Forward]
Acquisition	196
The Siam Commercial Samaggi Insurance PCL [Member] | Insurance - North American Agriculture
Goodwill [Roll Forward]
Acquisition	0
The Siam Commercial Samaggi Insurance PCL [Member] | Insurance - Overseas General
Goodwill [Roll Forward]
Acquisition	0
Large Corporate Property And Casualty Business Of Itau Seguros [Member] | Global Reinsurance
Goodwill [Roll Forward]
Acquisition	0
Large Corporate Property And Casualty Business Of Itau Seguros [Member] | Life
Goodwill [Roll Forward]
Acquisition	$ 0