SECURITIES - Income Recognized from Investment Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Interest Income, Securities, Operating, by Taxable Status [Abstract]
Taxable	$ 621	$ 619	$ 477
Non-taxable	0	0	0
Interest-bearing cash and due from banks and deposits in banks	5	5	11
Total interest income from investment securities and interest-bearing deposits in banks	626	624	488
Gain (Loss) on Sale of Investments [Abstract]
Gains on sale of debt securities	41	33	144
Losses on sale of debt securities	(12)	(5)	0
Debt securities gains, net	29	28	144
Equity securities gains	$ 3	$ 0	$ 0