Fair Value Measurements (Narrative) (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Net assets measured at fair value on a recurring basis	$ 2,500,000,000	$ 1,800,000,000
Net assets measured at fair value on a recurring basis measured using unobservable input and as Level 3	$ 1,000,000	$ (57,000,000)