Share Repurchase Programs and Dividends - Share Repurchase Programs (Detail) - USD ($)	12 Months Ended			42 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Equity [Abstract]
Stock repurchase programs, authorized amount	$ 11,000,000,000			$ 11,000,000,000
Stock repurchase programs, remaining authorized amount	$ 450,000,000			$ 450,000,000
Stock repurchased (in shares)	33,900,000	119,823,621	85,141,691	262,300,000
Aggregate stock repurchase price	$ 1,563,000,000	$ 4,416,000,000	$ 3,586,000,000	$ 10,600,000,000
Average cost per share (in dollars per share)	$ 45.68	$ 36.86	$ 42.09	$ 40.22