Consolidated Statements of Shareholders' Comprehensive Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Comprehensive Income
Shareholders' Net Income	$ 266	$ 560	$ 813	$ 598	$ 382	$ 456	$ 510	$ 519	$ 2,237	$ 1,867	$ 2,094
Shareholders' other comprehensive income (loss), net of tax:
Net unrealized appreciation (depreciation) on securities									(34)	(56)	(202)
Net unrealized appreciation (depreciation) on derivatives									(3)	(4)	15
Net translation of foreign currencies									304	(95)	(212)
Postretirement benefits liability adjustment									33	23	85
Shareholders' other comprehensive income (loss), net of tax									300	(132)	(314)
Shareholders' comprehensive income (loss)									$ 2,537	$ 1,735	$ 1,780