Computation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Basic earnings per share:
Earnings available to common stockholders	$ 1,193	$ 789	$ 1,701	$ 180
Basic weighted-average shares outstanding	380	373	381	371
Earnings per share, basic	$ 3.14	$ 2.12	$ 4.46	$ 0.48
Diluted earnings per share:
Earnings available to common stockholders	$ 1,193	$ 789	$ 1,701	$ 180
Effect of convertible notes		7		6
Earnings available to common stockholders including the effect of dilutive securities	$ 1,193	$ 796	$ 1,701	$ 186
Diluted shares outstanding:
Basic weighted-average shares outstanding	380	373	381	371
Effect of convertible notes		22		21
Effect of restricted stock and employee stock options		1	1
Diluted weighted-average shares outstanding	380	396	382	392
Earnings per share, diluted	$ 3.14	$ 2.01	$ 4.45	$ 0.47
Restricted Stock And Stock Options
Potentially dilutive shares excluded from diluted per share amounts:
Potentially dilutive shares excluded from diluted per share amounts		1		2
Convertible Notes
Potentially dilutive shares excluded from diluted per share amounts:
Potentially dilutive shares excluded from diluted per share amounts				4