Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended		3 Months Ended						9 Months Ended
	Feb. 29, 2016	Jan. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2016
Stockholders Equity [Abstract]
Net proceeds from offering									$ 1,469
Dividends paid per share			$ 0.06	$ 0.06	$ 0.24	$ 0.24	$ 0.24	$ 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]
Units issued for acquisition		23