Subsequent Events (Details) - USD ($) $ / shares in Units, shares in Millions							1 Months Ended	3 Months Ended				9 Months Ended
	Oct. 28, 2019	Oct. 24, 2019	Jul. 25, 2019	Apr. 29, 2019	Apr. 25, 2019	Jan. 29, 2019	Feb. 28, 2018	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 31, 2018
Dividends
Cash dividends declared per share of common stock (in dollars per share)			$ 0.19		$ 0.19	$ 0.19		$ 0.19		$ 0.18		$ 0.57	$ 0.54
Payment to repurchase stock												$ 354,900,000	$ 755,500,000
Common stock received, aggregate price								$ 111,100,000		$ 151,300,000		354,900,000	$ 755,500,000
Subsequent Event
Dividends
Cash dividends declared per share of common stock (in dollars per share)		$ 0.19
Stock Repurchase Program 2018
Dividends
Stock repurchase program, authorized amount								$ 1,700,000,000				$ 1,700,000,000		$ 2,000,000,000.0
Stock repurchased and retired (in shares)								5.1		6.0		13.7	29.3
Common stock received, aggregate price								$ 50,000,000.0		$ 0		$ 350,000,000.0	$ 750,000,000.0
Stock Repurchase Program 2018 | Subsequent Event
Dividends
Stock repurchase program, additional amount approved		$ 1,000,000,000.0
Accelerated Share Repurchase Program
Dividends
Stock repurchase program, authorized amount							$ 750,000,000.0
Payment to repurchase stock				$ 300,000,000.0			$ 750,000,000.0				$ 300,000,000.0
Stock repurchased and retired (in shares)									8.6			29.3
Common stock received, aggregate price											$ 240,000,000.0
Accelerated Share Repurchase Program | Subsequent Event
Dividends
Stock repurchase program, authorized amount	$ 200,000,000.0
Payment to repurchase stock	$ 200,000,000.0
Stock repurchased and retired (in shares)	6.4
Common stock received, aggregate price	$ 160,000,000.0