Consolidated Statements Of Operations and Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Revenues
Net premiums written	$ 5,995	$ 4,076
Decrease (increase) in unearned premiums	602	(149)
Net premiums earned	6,597	3,927
Net investment income	674	551
Net realized gains (losses):
Other-than-temporary impairment (OTTI) losses gross	(71)	(13)
Portion of OTTI losses recognized in other comprehensive income (OCI)	8	0
Net OTTI losses recognized in income	(63)	(13)
Net realized gains (losses) excluding OTTI losses	(331)	(76)
Total net realized gains (losses) (includes $(152) and $(3) reclassified from AOCI)	(394)	(89)
Total revenues	6,877	4,389
Expenses
Losses and loss expenses	3,674	2,122
Policy benefits	126	142
Policy acquisition costs	1,413	707
Administrative expenses	772	554
Interest expense	146	68
Other (income) expense	28	(35)
Amortization of purchased intangibles	7	30
Chubb integration expenses	148	0
Total expenses	6,314	3,588
Income before income tax	563	801
Income tax (benefits) expense (includes $(1) and $4 on reclassified unrealized gains and losses)	124	120
Net income	439	681
Other comprehensive income (loss)
Unrealized appreciation	905	441
Reclassification adjustment for net realized losses included in net income	152	3
Unrealized appreciation (Depreciation) after reclassification adjustment	1,057	444
Change in:
Cumulative translation adjustment	312	(421)
Pension liability	2	13
Other comprehensive income, before income tax	1,371	36
Income tax expense related to OCI items	(269)	(75)
Other comprehensive income (loss)	1,102	(39)
Comprehensive income	$ 1,541	$ 642
Earnings per share
Basic earnings per share	$ 0.98	$ 2.08
Diluted earnings per share	$ 0.97	$ 2.05
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Net realized gains (losses):
Total net realized gains (losses) (includes $(152) and $(3) reclassified from AOCI)	$ (152)	$ (3)
Expenses
Income tax (benefits) expense (includes $(1) and $4 on reclassified unrealized gains and losses)	$ (1)	$ 4