PARENT COMPANY ONLY FINANCIALS - Condensed Statements of Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Income
Interest income	$ 626	$ 624	$ 488
Total interest income	3,854	3,664	3,501
Operating expense
Salaries and employee benefits	1,636	1,678	1,652
Interest expense	452	363	443
All other expenses	530	573	528
Applicable income taxes	423	403	(42)
Net income (loss)	840	865	(3,426)
Other comprehensive (loss) income, net of income taxes
Reclassification of net securities gains to net income, net of income taxes of ($8), ($7), and ($50), respectively	(14)	(11)	(86)
Net unrealized securities (losses) gains arising during the period	(66)	198	(285)
Other comprehensive income activity of the Parent Company Only, net of income taxes	(15)	276	(336)
Total other comprehensive (loss) income, net of income taxes	(15)	276	(336)
Total comprehensive income (loss)	825	1,141	(3,762)
Payments of ordinary common stock dividends	214	806	1,200
Parent company
Operating Income
Dividends	345	595	210
Interest income	54	29	13
Management and service fees	20	21	26
Securities gains	3	0	0
All other operating income	4	5	2
Total interest income	426	650	251
Operating expense
Salaries and employee benefits	15	63	38
Interest expense	108	80	24
All other expenses	38	123	43
Total operating expense	161	266	105
Income before taxes and undistributed income	265	384	146
Applicable income taxes	(29)	(77)	(22)
Income before undistributed income of subsidiaries and associated companies	294	461	168
Equity in undistributed income (losses) of subsidiaries and associated companies	546	404	(3,594)
Net income (loss)	840	865	(3,426)
Other comprehensive (loss) income, net of income taxes
Net pension plan activity arising during the period	1	8	17
Reclassification of net securities gains to net income, net of income taxes of ($8), ($7), and ($50), respectively	2	0	1
Net unrealized securities (losses) gains arising during the period	(2)	1	0
Other comprehensive income activity of the Parent Company Only, net of income taxes	1	9	18
Other comprehensive income (loss) activity of Bank subsidiaries, net of income taxes	(16)	267	(354)
Total other comprehensive (loss) income, net of income taxes	(15)	276	(336)
Total comprehensive income (loss)	825	1,141	(3,762)
Bank Subsidiaries and Associated Banks | Parent company
Operating expense
Equity in undistributed income (losses) of subsidiaries and associated companies	543	402	(3,595)
Nonbank Subsidiaries and Associated Nonbank Companies | Parent company
Operating expense
Equity in undistributed income (losses) of subsidiaries and associated companies	$ 3	$ 2	$ 1