Equity - Common Stock Narrative (Details) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended		12 Months Ended
	Jan. 31, 2019	Dec. 31, 2018	Dec. 31, 2018	May 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Dividends declared per common share (in dollars per share)					$ 1.48	$ 1.480	$ 2.095
Maximum shares issuable under forward equity sales agreement (in shares)			15,250,000.00
Initial net price (in dollars per share)			$ 28.60
Management agreement renewal term (in years)			1 year
Subsequent Event
Subsequent Event [Line Items]
Dividends declared per common share (in dollars per share)	$ 0.37
At-The-Market Program
Subsequent Event [Line Items]
Maximum sales under equity offering program		$ 594		$ 750
Common stock issued (in shares)					5,400,000
Net price per share (in dollars per share)		$ 28.27	$ 28.27		$ 28.27
Proceeds from issuance of common stock					$ 154
Forward Equity Offering
Subsequent Event [Line Items]
Common stock issued (in shares)					0
Common Stock
Subsequent Event [Line Items]
Common stock issued (in shares)			2,000,000
Net price per share (in dollars per share)		$ 28.60	$ 28.60		$ 28.60
Proceeds from issuance of common stock			$ 57