Equity Other Equity Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Class of Stock [Line Items]
Proceeds from Issuance of Common Stock	$ 843	$ 22
2015 ATM Program, Life to Date Proceeds, Gross	350
2015 ATM Program, capacity remaining	$ 150
Preferred Stock, Par or Stated Value Per Share	$ 0.01		$ 0.01
2015 ATM, Aggregate Value of Common Stock	$ 500
March 2018 Equity Financing [Member]
Class of Stock [Line Items]
Proceeds from Issuance of Common Stock	$ 840
Stock Issued During Period, Shares, New Issues	8
Common Stock [Member]
Class of Stock [Line Items]
Proceeds from Issuance of Common Stock	$ 0
Stock Issued During Period, Shares, New Issues	8	0