Available-For-Sale Securities (Narrative) (Detail) (USD $) In Billions, unless otherwise specified	Mar. 31, 2015 securities	Dec. 31, 2014	Mar. 31, 2014
Available-for-sale Securities [Abstract]
Pledged Securities, carrying value	$ 1.1	$ 1.1	$ 1.2
Number of securities by a single non-goverment sponsored issuer exceeding 10% of shareholders' equity	0