Stockholders' Equity - Summary of Repurchase Activity (Details) - USD ($)		12 Months Ended
	Feb. 13, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 31, 2020	Jan. 31, 2019
Equity, Class of Treasury Stock [Line Items]
Shares Repurchased (in shares)		50,000,000
Average Price per Share (in usd per share)		$ 42.09
Value of Shares Repurchased		$ 2,118,000,000
Shares Repurchased, Remaining Amount Authorized
Beginning balance		2,151,000,000
Authorization of additional plan in January 2020					$ 5,000,000,000.0	$ 4,000,000,000.0
Repurchase of shares of common stock		(2,118,000,000)
Ending balance		$ 2,033,000,000	$ 2,151,000,000
Treasury shares retired (in shares)		0
Treasury stock at cost
Equity, Class of Treasury Stock [Line Items]
Value of Shares Repurchased		$ 5,119,000,000	5,002,000,000	$ 4,502,000,000
Shares Repurchased, Remaining Amount Authorized
Repurchase of shares of common stock		(5,119,000,000)	$ (5,002,000,000)	$ (4,502,000,000)
Accelerated share repurchases
Equity, Class of Treasury Stock [Line Items]
Shares Repurchased (in shares)	69,000,000
Value of Shares Repurchased	$ 3,000,000,000.0	450,000,000
Shares Repurchased, Remaining Amount Authorized
Repurchase of shares of common stock	(3,000,000,000.0)	$ (450,000,000)
Accelerated share repurchases | Treasury stock at cost
Equity, Class of Treasury Stock [Line Items]
Shares Repurchased (in shares)		74,000,000
Average Price per Share (in usd per share)		$ 40.77
Value of Shares Repurchased	2,550,000,000	$ 3,000,000,000
Shares Repurchased, Remaining Amount Authorized
Repurchase of shares of common stock	$ (2,550,000,000)	$ (3,000,000,000)