Consolidated Statements Of Shareholders' Equity (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Consolidated Statements Of Shareholders Equity [Abstract]
Change in year, before reclassification from AOCI, net of income tax benefit(expense)	$ 226	$ (102)
Income tax benefit (expense) from reclassification of unrealized gains	(3)	(6)
Net unrealized appreciation on investments, Change in period, income tax (expense) benefit	223	(108)
Cumulative translation adjustment, Change in period, income tax(expense) benefit	(19)	(3)
Net income	1,082	1,093
Pension liability adjustment, Change in period, income tax (expense) benefit	$ 4	$ (4)