DISCONTINUED OPERATIONS AND SIGNIFICANT DISPOSALS - Significant Disposals (Details) $ in Millions			3 Months Ended		6 Months Ended
	Sep. 30, 2014 USD ($) employee branch atm	Sep. 22, 2014 USD ($) employee branch atm	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Disposal Group, Held-for-sale, Not Discontinued Operations
Assets
Cash and deposits with banks			$ 533		$ 533		$ 151
Investments			1,444		1,444		0
Loans, net			9,419		9,419		544
Allowance			708		708		2
Goodwill			112		112		51
Intangible assets			152		152		0
Other assets, advances to/from subs			19,286		19,286		19,854
Other assets			492		492		66
Total assets			31,438		31,438		20,666
Liabilities
Deposits			19,982		19,982		20,605
Long-term debt			5,923		5,923		0
Other liabilities, due to/from subs			2,033		2,033		0
Other liabilities			1,963		1,963		61
Total liabilities			29,901		29,901		20,666
Disposal Group, Held-for-sale, Not Discontinued Operations | OneMain Financial Business
Discontinued operations
Income before taxes			168	$ 226	346	$ 487
Assets
Cash and deposits with banks			420		420
Investments			1,444		1,444
Loans, net			7,533		7,533
Allowance			684		684
Intangible assets			152		152
Other assets			361		361
Total assets			9,910		9,910
Liabilities
Long-term debt			5,923		5,923
Other liabilities, due to/from subs			2,033		2,033
Other liabilities			1,453		1,453
Total liabilities			9,409		9,409
Disposal Group, Held-for-sale, Not Discontinued Operations | Japan Cards Business
Discontinued operations
Income before taxes			10	(1)	9	(1)
Assets
Cash and deposits with banks			16		16
Loans, net			1,341		1,341
Allowance			23		23
Goodwill			61		61
Other assets			73		73
Total assets			1,491		1,491
Liabilities
Other liabilities			455		455
Total liabilities			455		455
Disposal Group, Held-for-sale, Not Discontinued Operations | Japan Retail Business
Discontinued operations
Income before taxes			20	(2)	20	0
Assets
Cash and deposits with banks			97		97		151
Loans, net			545		545		544
Allowance			1		1		2
Goodwill			51		51		51
Other assets, advances to/from subs			19,286		19,286		19,854
Other assets			58		58		66
Total assets			20,037		20,037		20,666
Liabilities
Deposits			19,982		19,982		20,605
Other liabilities			55		55		61
Total liabilities			20,037		20,037		$ 20,666
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Spain Consumer Business
Discontinued operations
Income before taxes			0	12	0	33
Assets
Loans, net		$ 1,700
Liabilities
Deposits		2,200
Additional Disclosures
Assets under management		$ 3,400
Number of branches | branch		45
Number of ATMs | atm		48
Number of employees | employee		938
Pre-tax gain on sale		$ 243
After tax gain on sale of discontinued operations		$ 131
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Greece Consumer Business
Discontinued operations
Income before taxes			$ 0	$ (25)	$ 0	$ (40)
Assets
Loans, net	$ 353
Liabilities
Deposits	1,200
Additional Disclosures
Assets under management	$ 1,100
Number of branches | branch	20
Number of ATMs | atm	85
Number of employees | employee	719
Pre-tax gain on sale	$ 209
After tax gain on sale of discontinued operations	$ 91