Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Stock Issued During Period, Shares, New Issues									0	0	136,951,452
Net income	$ 355	$ 1,231	$ 1,294	$ 1,082	$ 1,533	$ (70)	$ 1,305	$ 1,093	$ 3,962	$ 3,861	$ 4,135
Weighted-average shares outstanding									463,629,203	467,145,716	462,519,789
Share-based compensation plans									3,173,145	4,051,185	3,429,610
Adjusted weighted-average shares outstanding and assumed conversions									466,802,348	471,196,901	465,949,399
Basic earnings per share	$ 0.77	$ 2.66	$ 2.78	$ 2.32	$ 3.29	$ (0.15)	$ 2.79	$ 2.33	$ 8.55	$ 8.26	$ 8.94
Diluted earnings per share	$ 0.76	$ 2.64	$ 2.76	$ 2.30	$ 3.27	$ (0.15)	$ 2.77	$ 2.31	$ 8.49	$ 8.19	$ 8.87
Potential anti-dilutive share conversions									3,543,188	1,776,025	1,206,828