Shareholders' Equity - Narrative (Details) - USD ($)			3 Months Ended
	Nov. 30, 2018	Nov. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Nov. 19, 2018	Nov. 13, 2018
Class of Stock [Line Items]
Gross proceeds from equity offering		$ 400,000,000
Net proceeds from equity offering		$ 395,100,000	$ 494,734,000	$ 395,099,000
Forward sales equity agreement, shares	2,668,464
Forward sales equity agreement, settlement date			Mar. 31, 2020
Forward sales equity agreement, settlements			$ 0
Forward sales equity agreement, settlement alternatives, cash, at fair value			$ 245,200,000
Forward sales equity agreement, forward rate per share			$ 91.90
Shelf Registration Statement
Class of Stock [Line Items]
Debt and equity securities authorized for issuance						$ 3,000,000,000
Debt and equity securities authorized for issuance value remaining			$ 1,800,000,000
At-The-Market
Class of Stock [Line Items]
Value of shares authorized for issuance					$ 500,000,000
Stock Issued During Period, New Issues (in shares)			0
Common Stock Block Trade
Class of Stock [Line Items]
Stock Issued During Period, New Issues (in shares)	5,390,836	4,558,404
Gross proceeds from equity offering	$ 500,000,000
Net proceeds from equity offering	$ 494,700,000