Earnings Per Share - Narrative (Details) - USD ($) shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jul. 15, 2019
Earnings Loss Per Share [Line Items]
Repurchases of common stock	$ 536,000,000	$ 407,000,000	$ 1,063,000,000	$ 976,000,000
Open Market Repurchase Program
Earnings Loss Per Share [Line Items]
Number of shares repurchased (in shares)	6.4		12.7
Repurchases of common stock	$ 500,000,000		$ 1,100,000,000
Amount remaining under repurchase programs	$ 700,000,000		$ 700,000,000
Subsequent Event [Member] | July 2019 Share Repurchase Program [Member]
Earnings Loss Per Share [Line Items]
Authorized amount under share repurchase program					$ 3,000,000,000.0