Fair Value of Financial Assets and Liabilities - Changes In Fair Value of Level 3 Financial Assets (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Other-than-temporary impairment loss	$ (24)	$ (33)	$ 0	$ 0
Auction rate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ (34)	$ (8)