Taxation (Reconciliation Of The Difference Between The Provision for Income Taxes and the Expected Tax Provision at Swiss Statutory Income Tax Rate) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Expected tax provision at Swiss statutory rate	$ 291	$ 388	$ 258
Taxes on earnings subject to rates other that Swiss statutory rate	263	582	193
Tax exempt interest and dividends received deduction, net of proration	(199)	(200)	(32)
Net witholding taxes	30	20	35
Change in valuation allowance	(48)	0	0
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	(450)
Income tax benefit related to 2017 Tax Act	(450)	0	0
Income Tax Reconciliation, Non-taxable Acquisition Gain	(37)	0	0
Other	11	25	8
Provision for income taxes	$ (139)	$ 815	$ 462