Stock Repurchase Programs (Details) - USD ($)	1 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2018	Apr. 30, 2017	Jan. 31, 2016
Equity, Class of Treasury Stock [Line Items]
Repurchases of shares of common stock, shares repurchased (in shares)		14,000,000	44,000,000	20,000,000
Cash paid for shares repurchased		$ 1,411,000,000	$ 3,520,000,000	$ 1,006,000,000
Repurchased shares retired during period (in shares)		0	0	0
January 2016 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, maximum authorized amount							$ 2,000,000,000
April 2017 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, maximum authorized amount						$ 5,000,000,000
Remaining amount authorized for future repurchase of common stock		$ 68,000,000
July 2018 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Remaining amount authorized for future repurchase of common stock		10,000,000,000			$ 10,000,000,000
Open Market Transactions
Equity, Class of Treasury Stock [Line Items]
Cash paid for shares repurchased		656,000,000	$ 2,500,000,000	$ 1,000,000,000.0
Accelerated Share Repurchase Agreement
Equity, Class of Treasury Stock [Line Items]
Repurchases of shares of common stock, shares repurchased (in shares)	7,700,000
Cash paid for shares repurchased		$ 750,000,000	$ 1,000,000,000.0
Repurchases of shares of common stock, value of shares repurchased	$ 750,000,000
Repurchases of shares of common stock, average price paid per share (in usd per share)	$ 96.91