PARENT COMPANY ONLY FINANCIALS - Condensed Cash Flow Statements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING ACTIVITIES
Net income (loss)	$ 840	$ 865	$ (3,426)
Deferred income taxes	249	141	(53)
Gain on sales of assets	0	9	0
Net change in other liabilities	(161)	239	(398)
Net change in other assets	(467)	(295)	827
Net cash provided by operating activities	1,229	1,390	2,649
INVESTING ACTIVITIES
Net cash used in investing activities	(5,905)	(10,274)	(2,453)
FINANCING ACTIVITIES
Repayments of long-term borrowed funds (related party balances of $750, $0 and $280, respectively)	(766)	(6)	(291)
Repurchase of common stock	(500)	(334)	0
Proceeds from issuance of preferred stock	247	0	0
Dividends paid	(71)	(790)	(1,185)
Net cash provided by (used in) financing activities	4,485	9,403	(502)
Cash and cash equivalents at beginning of period	3,276	2,757	3,063
(Decrease) increase in cash and cash equivalents	(191)	519	(306)
Cash and cash equivalents at end of period	3,085	3,276	2,757
Parent company
OPERATING ACTIVITIES
Net income (loss)	840	865	(3,426)
Deferred income taxes	49	27	(11)
Gain on sales of assets	(3)	0	0
Equity in undistributed (earnings) losses of subsidiaries	(546)	(404)	3,594
Net change in other liabilities	(48)	18	7
Net change in other assets	(16)	(74)	15
Other operating, net	3	17	1
Total adjustments	(561)	(416)	3,606
Net cash provided by operating activities	279	449	180
INVESTING ACTIVITIES
Proceeds from sales and maturities of securities available for sale	8	0	0
Payments for investments in and advances to subsidiaries	(215)	(1,470)	(220)
Sale or repayment of investments in and advances to subsidiaries	376	945	315
Other investing, net	0	(11)	(1)
Net cash used in investing activities	169	(536)	94
FINANCING ACTIVITIES
Repayment of advances from subsidiaries	0	0	(289)
Proceeds from issuance of long-term debt	1,000	1,000	1,000
Repayments of long-term borrowed funds (related party balances of $750, $0 and $280, respectively)	(750)	0	0
Proceeds from issuance of common stock	27	13	0
Repurchase of common stock	(500)	(334)	0
Proceeds from issuance of preferred stock	247	0	0
Dividends paid	(221)	(806)	(1,185)
Net cash provided by (used in) financing activities	(197)	(127)	(474)
Cash and cash equivalents at beginning of period	280	494	694
(Decrease) increase in cash and cash equivalents	251	(214)	(200)
Cash and cash equivalents at end of period	$ 531	$ 280	$ 494