Consolidated Statements of Changes in Shareholders' Equity (USD $) In Millions, unless otherwise specified	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss, Net [Member]
Balance at Dec. 31, 2011	$ 7,312	$ 41	$ 0	$ 4,479	$ 2,801	$ (9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	537				537
Other comprehensive income (loss)	(3)					(3)
Preferred stock dividends declared	(2)				(2)
Common stock dividends declared	(200)				(200)
Balance at Dec. 31, 2012	7,644	41	0	4,479	3,136	(12)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	682				682
Other comprehensive income (loss)	3					3
Preferred stock dividends declared	(2)				(2)
Common stock dividends declared	(500)				(500)
Redemption of preferred stock	(40)	(39)			(1)
Balance at Dec. 31, 2013	7,787	2	0	4,479	3,315	(9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	698				698
Other comprehensive income (loss)	(4)					(4)
Common stock dividends declared	(725)				(725)
Balance at Dec. 31, 2014	$ 7,756	$ 2	$ 0	$ 4,479	$ 3,288	$ (13)