Investments (Schedule Of Components Of Restricted Assets) (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Trust funds	$ 17,029	$ 17,011
Deposits with U.S. regulatory authorities	2,463	2,345
Deposits with non-U.S. regulatory authorities	2,290	2,250
Assets pledged under repurchase agreements	1,460	1,434
Other pledged assets	433	414
Total restricted assets	$ 23,675	$ 23,454