Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended		3 Months Ended				6 Months Ended
	Feb. 29, 2016	Jan. 31, 2016	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2016
Stockholders Equity [Abstract]
Net proceeds from offering							$ 1,469
Common stock dividends, rate per share			$ 0.06	$ 0.06	$ 0.06	$ 0.24
Common Stock [Member]
Stockholders Equity [Abstract]
Common stock, shares issued							103
Common Stock Offering [Member]
Stockholders Equity [Abstract]
Common stock, shares issued	79
Net proceeds from offering	$ 1,500
Common Stock Offering [Member] | Underwriters [Member]
Stockholders Equity [Abstract]
Common stock, shares issued	10
Equity Issued in Business Combination [Member] | Common Stock [Member] | STACK [Member]
Stockholders Equity [Abstract]
Equity issued for acquisition		23