Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 751	$ 870	$ 939	$ 908	$ 640	$ 795	$ 782	$ 671	$ 3,468	$ 2,888	$ 4,536
Less: Dividends on mandatory convertible preferred stock									0	0	(55)
Net income attributable to common stockholders	$ 751	$ 870	$ 939	$ 908	$ 640	$ 795	$ 782	$ 671	3,468	2,888	4,481
Add: Dividends related to mandatory convertible preferred stock									0	0	55
Net income attributable to common stockholders									$ 3,468	$ 2,888	$ 4,536
Weighted average shares outstanding - basic (in shares)	856,294,467	854,578,241	854,368,443	851,223,498	849,102,785	847,087,120	847,660,488	855,222,664	854,143,751	849,744,152	831,850,073
Effect of dilutive securities:
Outstanding stock options and unvested stock awards (in shares)									9,289,760	8,546,022	9,200,873
Mandatory convertible preferred stock (in shares)									0	0	30,736,504
Weighted average shares outstanding - diluted (in shares)	864,158,739	862,690,751	860,135,593	858,643,481	856,344,347	853,852,764	852,040,670	862,244,084	863,433,511	858,290,174	871,787,450
Earnings per share - basic (in USD per share)	$ 0.88	$ 1.02	$ 1.10	$ 1.07	$ 0.75	$ 0.94	$ 0.92	$ 0.78	$ 4.06	$ 3.40	$ 5.39
Earnings per share - diluted (in USD per share)	$ 0.87	$ 1.01	$ 1.09	$ 1.06	$ 0.75	$ 0.93	$ 0.92	$ 0.78	$ 4.02	$ 3.36	$ 5.20
Outstanding stock options and unvested stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities (in shares)									16,359	148,422	33,980