Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	OPIC	AOCI	Accumulated Deficit
Beginning balance, (in shares) at Dec. 31, 2019		541,000,000
Beginning balance at Dec. 31, 2019	$ 6,975	$ 54	$ 10,868	$ 20	$ (3,967)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	74				74
Other comprehensive loss, net of tax	(18)			(18)
Stock Investment Plan and share-based benefit plans (in shares)		1,000,000
Stock Investment Plan and share-based benefit plans	(6)		(6)
Cash dividends declared on common stock	(211)		(211)
Ending balance (in shares) at Mar. 31, 2020		542,000,000
Ending balance at Mar. 31, 2020	$ 6,814	$ 54	10,651	2	(3,893)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.39
Beginning balance, (in shares) at Dec. 31, 2019		541,000,000
Beginning balance at Dec. 31, 2019	$ 6,975	$ 54	10,868	20	(3,967)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	837
Other comprehensive loss, net of tax	(22)
Ending balance (in shares) at Sep. 30, 2020		543,000,000
Ending balance at Sep. 30, 2020	7,188	$ 54	10,266	(2)	(3,130)
Beginning balance, (in shares) at Mar. 31, 2020		542,000,000
Beginning balance at Mar. 31, 2020	6,814	$ 54	10,651	2	(3,893)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	309				309
Other comprehensive loss, net of tax	(2)			(2)
Stock Investment Plan and share-based benefit plans	22		22
Ending balance (in shares) at Jun. 30, 2020		542,000,000
Ending balance at Jun. 30, 2020	7,143	$ 54	10,673	0	(3,584)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	454				454
Other comprehensive loss, net of tax	(2)			(2)
Stock Investment Plan and share-based benefit plans	17	$ 1	17
Cash dividends declared on common stock	(424)		(424)
Ending balance (in shares) at Sep. 30, 2020		543,000,000
Ending balance at Sep. 30, 2020	$ 7,188	$ 54	10,266	(2)	(3,130)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.39
Beginning balance, (in shares) at Dec. 31, 2020	543,117,533	543,000,000
Beginning balance at Dec. 31, 2020	$ 7,237	$ 54	10,076	(5)	(2,888)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	335				335
Other comprehensive loss, net of tax	(2)			(2)
Share-based benefit plans (in shares)		1,000,000
Share-based benefit plans	2		2
Cash dividends declared on common stock	(212)		(212)
Ending balance (in shares) at Mar. 31, 2021		544,000,000
Ending balance at Mar. 31, 2021	$ 7,360	$ 54	9,866	(7)	(2,553)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.39
Beginning balance, (in shares) at Dec. 31, 2020	543,117,533	543,000,000
Beginning balance at Dec. 31, 2020	$ 7,237	$ 54	10,076	(5)	(2,888)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	856
Other comprehensive loss, net of tax	$ (6)
Ending balance (in shares) at Sep. 30, 2021	544,419,619	544,000,000
Ending balance at Sep. 30, 2021	$ 7,479	$ 54	9,468	(11)	(2,032)
Beginning balance, (in shares) at Mar. 31, 2021		544,000,000
Beginning balance at Mar. 31, 2021	7,360	$ 54	9,866	(7)	(2,553)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	58				58
Other comprehensive loss, net of tax	(2)			(2)
Share-based benefit plans	14		14
Ending balance (in shares) at Jun. 30, 2021		544,000,000
Ending balance at Jun. 30, 2021	7,430	$ 54	9,880	(9)	(2,495)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	463				463
Other comprehensive loss, net of tax	(2)			(2)
Share-based benefit plans (in shares)
Share-based benefit plans	13		13
Cash dividends declared on common stock	$ (425)		(425)
Ending balance (in shares) at Sep. 30, 2021	544,419,619	544,000,000
Ending balance at Sep. 30, 2021	$ 7,479	$ 54	$ 9,468	$ (11)	$ (2,032)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.39