Shareholders' Equity - Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands	1 Months Ended	9 Months Ended
	Jul. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity, Class of Treasury Stock [Line Items]
Proceeds from issuance of common stock		$ 1,150,000,000	$ 0
2017 Program
Equity, Class of Treasury Stock [Line Items]
Amount of common stock authorized for repurchase					$ 1,400,000,000.0
Shares Acquired		3,300
Average Cost per Share (USD per share)		$ 105.31
Total Acquired		$ 350,000,000
2018 Program
Equity, Class of Treasury Stock [Line Items]
Amount of common stock authorized for repurchase				$ 1,200,000,000.0
Common Stock
Equity, Class of Treasury Stock [Line Items]
Shares issued (shares)	13,240
Offering price of shares issued (USD per share)	$ 86.93
Proceeds from issuance of common stock	$ 1,150,000,000