Investments (Schedule Of Components Of Restricted Assets) (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Trust funds	$ 14,359	$ 13,880
Deposits with U.S. regulatory authorities	2,356	2,203
Deposits with non-U.S. regulatory authorities	2,192	2,191
Assets pledged under repurchase agreements	1,453	1,461
Other pledged assets	366	435
Total restricted assets	$ 20,726	$ 20,170