Consolidated Statements of Shareholders' Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement Of Comprehensive Income [Abstract]
Shareholders' Net Income	$ 456	$ 547	$ 1,485	$ 1,668
Shareholders' other comprehensive income (loss):
Net unrealized appreciation (depreciation) on securities	66	8	416	(138)
Net unrealized appreciation (depreciation), derivatives	(1)	3	(5)	15
Net translation of foreign currencies	55	(112)	96	(198)
Postretirement benefits liability adjustment	9	11	28	42
Shareholders' other comprehensive income (loss)	129	(90)	535	(279)
Shareholders' comprehensive income (loss)	$ 585	$ 457	$ 2,020	$ 1,389