CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions	Total	Common Stock	Additional Paid In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Common Stock, Dividends, Per Share, Declared	$ 0.76
Beginning balance at Dec. 31, 2017	$ 11,455	$ 1,269	$ 5,898	$ 4,413	$ (125)
Balance (in shares) at Dec. 31, 2017		507,763,000
Increase (Decrease) in Stockholders' Equity
Net income	556			556
Other comprehensive income	3				3
Dividends declared on common stock	(389)			(389)
Issuances of common stock (in shares)		1,157,000
Stock Repurchased During Period, Shares		(22,000)
Stock Repurchased During Period, Value	(1)	$ 0	(1)
Issuances of common stock	27	3	24
Share-based compensation	(1)		(1)	0
Ending balance at Jun. 30, 2018	$ 11,650	$ 1,272	5,920	4,580	(122)
Balance (in shares) at Jun. 30, 2018		508,898,000
Common Stock, Dividends, Per Share, Declared	$ 0.38
Beginning balance at Mar. 31, 2018	$ 11,561	$ 1,272	5,903	4,510	(124)
Balance (in shares) at Mar. 31, 2018		508,662,000
Increase (Decrease) in Stockholders' Equity
Net income	265			265
Other comprehensive income	2				2
Dividends declared on common stock	(195)			(195)
Issuances of common stock (in shares)		236,000
Issuances of common stock	10	$ 0	10
Share-based compensation	7		7	0
Ending balance at Jun. 30, 2018	$ 11,650	$ 1,272	5,920	4,580	(122)
Balance (in shares) at Jun. 30, 2018		508,898,000
Common Stock, Dividends, Per Share, Declared	$ 0.81
Beginning balance at Dec. 31, 2018	$ 12,222	$ 1,285	6,168	4,893	(124)
Balance (in shares) at Dec. 31, 2018	514,036,787	514,037,000
Increase (Decrease) in Stockholders' Equity
Net income	$ 553			553
Other comprehensive income	(11)				(11)
Dividends declared on common stock	(419)			(419)
Issuances of common stock (in shares)		834,000
Stock Repurchased During Period, Shares		(6,000)
Stock Repurchased During Period, Value	0	$ 0	0
Issuances of common stock	22	2	20
Share-based compensation	(1)		2	(3)
Ending balance at Jun. 30, 2019	$ 12,366	$ 1,287	6,190	5,024	(135)
Balance (in shares) at Jun. 30, 2019	514,865,476	514,865,000
Common Stock, Dividends, Per Share, Declared	$ 0.41
Beginning balance at Mar. 31, 2019	$ 12,329	$ 1,287	6,173	4,996	(127)
Balance (in shares) at Mar. 31, 2019		514,668,000
Increase (Decrease) in Stockholders' Equity
Net income	238			238
Other comprehensive income	(8)				(8)
Dividends declared on common stock	(209)			(209)
Issuances of common stock (in shares)		197,000
Issuances of common stock	10	$ 0	10
Share-based compensation	6		7	(1)
Ending balance at Jun. 30, 2019	$ 12,366	$ 1,287	$ 6,190	$ 5,024	$ (135)
Balance (in shares) at Jun. 30, 2019	514,865,476	514,865,000