CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) shares in Millions, $ in Millions	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock, at Cost	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2014		0	546
Beginning balance at Dec. 31, 2014	$ 19,268	$ 0	$ 6	$ 18,676	$ 1,294	$ (336)	$ (372)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to common stockholders	(48)				(48)
Dividends to RBS	(60)				(60)
Issuance of preferred stock (in shares)		0
Issuance of preferred stock, value	247	$ 247
Treasury stock purchased (in shares)			(10)
Treasury stock purchased	(250)					(250)
Share-based compensation plans (in shares)			1
Share-based compensation plans	13			34		(21)
Employee stock purchase plan shares purchased	4			4
Total comprehensive income:
Net income	399				399
Other comprehensive income	13						13
Total comprehensive income	412				399		13
Ending balance (in shares) at Jun. 30, 2015		0	537
Ending balance at Jun. 30, 2015	19,586	$ 247	$ 6	18,714	1,585	(607)	(359)
Beginning balance at Mar. 31, 2015							(240)
Total comprehensive income:
Other comprehensive income							(119)
Total comprehensive income	71
Ending balance (in shares) at Jun. 30, 2015		0	537
Ending balance at Jun. 30, 2015	19,586	$ 247	$ 6	18,714	1,585	(607)	(359)
Beginning balance (in shares) at Dec. 31, 2015		0	528
Beginning balance at Dec. 31, 2015	19,646	$ 247	$ 6	18,725	1,913	(858)	(387)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends to common stockholders	(117)				(117)
Dividend to preferred stockholders	(7)				(7)
Share-based compensation plans (in shares)			1
Share-based compensation plans	5			5
Employee stock purchase plan shares purchased	5			5
Total comprehensive income:
Net income	466				466
Other comprehensive income	228						228
Total comprehensive income	694				466		228
Ending balance (in shares) at Jun. 30, 2016		0	529
Ending balance at Jun. 30, 2016	20,226	$ 247	$ 6	18,735	2,255	(858)	(159)
Beginning balance at Mar. 31, 2016							(236)
Total comprehensive income:
Other comprehensive income							77
Total comprehensive income	320
Ending balance (in shares) at Jun. 30, 2016		0	529
Ending balance at Jun. 30, 2016	$ 20,226	$ 247	$ 6	$ 18,735	$ 2,255	$ (858)	$ (159)