Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Stock Issued During Period, Shares, New Issues									0	136,951,452	0
Net income	$ 1,533	$ (70)	$ 1,305	$ 1,093	$ 1,610	$ 1,360	$ 726	$ 439	$ 3,861	$ 4,135	$ 2,834
Weighted-average shares outstanding									467,145,716	462,519,789	325,589,361
Share-based compensation plans									4,051,185	3,429,610	3,246,017
Adjusted weighted-average shares outstanding and assumed conversions									471,196,901	465,949,399	328,835,378
Basic earnings per share	$ 3.29	$ (0.15)	$ 2.79	$ 2.33	$ 3.44	$ 2.90	$ 1.55	$ 0.98	$ 8.26	$ 8.94	$ 8.71
Diluted earnings per share	$ 3.27	$ (0.15)	$ 2.77	$ 2.31	$ 3.41	$ 2.88	$ 1.54	$ 0.97	$ 8.19	$ 8.87	$ 8.62
Potential anti-dilutive share conversions									1,776,025	1,206,828	1,601,668