CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total	Common stock	Additional Paid In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Balance (in shares) at Dec. 31, 2016		507,223,000
Beginning balance at Dec. 31, 2016	$ 11,021	$ 1,268	$ 5,881	$ 3,982	$ (110)
Increase (Decrease) in Stockholders' Equity
Net income	1,148			1,148
Other comprehensive income	7				7
Dividends declared on common stock	(736)			(736)
Issuances of common stock (in shares)		611,000
Issuances of common stock (value)	5	$ 1	4
Stock repurchased during period (in shares)		(71,000)
Repurchases of common stock (value)	(3)	$ 0	(3)
Share-based compensation	13		16	(3)
Adoption of ASU No. 2018-02	0			22	(22)
Balance (in shares) at Dec. 31, 2017		507,763,000
Ending balance at Dec. 31, 2017	11,455	$ 1,269	5,898	4,413	(125)
Increase (Decrease) in Stockholders' Equity
Net income	1,261			1,261
Other comprehensive income	1				1
Dividends declared on common stock	(780)			(780)
Issuances of common stock (in shares)		6,296,000
Issuances of common stock (value)	270	$ 16	254
Stock repurchased during period (in shares)		(22,000)
Repurchases of common stock (value)	(1)	$ 0	(1)
Share-based compensation	$ 16		17	(1)
Balance (in shares) at Dec. 31, 2018	514,036,787	514,037,000
Ending balance at Dec. 31, 2018	$ 12,222	$ 1,285	6,168	4,893	(124)
Increase (Decrease) in Stockholders' Equity
Net income	1,372			1,372
Other comprehensive income	(17)				(17)
Dividends declared on common stock	(846)			(846)
Issuances of common stock (in shares)		10,508,000
Issuances of common stock (value)	494	$ 26	468
Stock repurchased during period (in shares)		(6,000)
Repurchases of common stock (value)	0	$ 0	0
Share-based compensation	$ 14		20	(6)
Balance (in shares) at Dec. 31, 2019	524,539,000	524,539,000
Ending balance at Dec. 31, 2019	$ 13,239	$ 1,311	$ 6,656	$ 5,413	$ (141)