Defined Benefit Plan Assets Measured at Fair Value Using Unobservable Inputs (Level Three) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Balance at beginning of year	$ 293	$ 256
Actual return on plan assets, Sold during the year	7	15
Actual return on plan assets, Held at year end	6	7
Purchases, sales, issuances and settlements (net)	6	15
Balance at end of year	$ 312	$ 293