Consolidated Statements Of Operations and Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues
Net premiums written	$ 7,104	$ 6,710
Change In Unearned Premium Net	77	(62)
Net premiums earned	7,027	6,772
Net investment income	806	745
Net Realized Gains Losses [Abstract]
Other-than-temporary impairment (OTTI) losses gross	(1)	(19)
Portion of OTTI losses recognized in other comprehensive income (OCI)	0	0
Net OTTI losses recognized in income	(1)	(19)
Net realized gains (losses) excluding OTTI losses	(1)	12
Total net realized gains (losses) (includes $(23) and $(8) reclassified from AOCI)	(2)	(7)
Total revenues	7,831	7,510
Expenses
Losses and loss expenses	4,102	3,789
Policy benefits	151	168
Policy acquisition costs	1,464	1,397
Administrative expenses	692	676
Interest expense	157	154
Other (income) expense	(47)	(70)
Amortization of purchased intangibles	85	64
Chubb integration expenses	10	111
Total expenses	6,614	6,289
Income before income tax	1,217	1,221
Income tax expense (benefit) (includes $(3) and $(6) on reclassified unrealized losses)	135	128
Net income	1,082	1,093
Other comprehensive income (loss)
Unrealized appreciation (depreciation)	(1,234)	307
Reclassification adjustment for net realized losses included in net income	23	8
Unrealized appreciation (Depreciation) after reclassification adjustment	(1,211)	315
Change in:
Cumulative foreign currency translation adjustment	397	134
Postretirement benefit liability adjustment	(23)	(20)
Other comprehensive income (loss), before income tax	(837)	429
Income tax (expense) benefit related to OCI items	208	(115)
Other comprehensive income (loss)	(629)	314
Comprehensive income	$ 453	$ 1,407
Earnings per share
Basic earnings per share	$ 2.32	$ 2.33
Diluted earnings per share	$ 2.30	$ 2.31