Computation of Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Basic earnings per share:
Net income	$ 924	$ 379	$ 1,104	$ 431
Less: Income allocable to participating securities	(1)	(1)	(2)	(1)
Earnings available to common stockholders	923	378	1,102	430
Basic weighted-average shares outstanding	370	357	370	343
Earnings per share, basic	$ 2.49	$ 1.06	$ 2.97	$ 1.25
Diluted earnings per share:
Earnings available to common stockholders	923	378	1,102	430
Effect of convertible notes	6	9	20	20
Earnings available to common stockholders including the effect of dilutive securities	$ 929	$ 387	$ 1,122	$ 450
Diluted shares outstanding:
Basic weighted-average shares outstanding	370	357	370	343
Effect of convertible notes	22	37	24	46
Effect of employee stock options		1	1	1
Diluted weighted-average shares outstanding	392	395	395	390
Earnings per share, diluted	$ 2.37	$ 0.98	$ 2.84	$ 1.15
Restricted Stock And Stock Options
Potentially dilutive shares excluded from diluted per share amounts:
Potentially dilutive shares excluded from diluted per share amounts	1	3	1	3
Convertible Notes
Potentially dilutive shares excluded from diluted per share amounts:
Potentially dilutive shares excluded from diluted per share amounts				4