Share Repurchase Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended				58 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	May 31, 2014	Mar. 31, 2013
Equity Class Of Treasury Stock [Line Items]
Repurchase of outstanding common stock						$ 6,500	$ 4,000
Additional amount of common stock that may be repurchased		$ 1,030			$ 1,030
Common stock to be repurchased		$ 120	$ 0	$ 91	$ 5,471
Scenario Forecast
Equity Class Of Treasury Stock [Line Items]
Common stock to be repurchased	$ 380