PREFERRED STOCK (Details) $ / shares in Units, $ in Millions														3 Months Ended	6 Months Ended		12 Months Ended
	Apr. 24, 2015	Mar. 20, 2015	Oct. 29, 2014	Apr. 30, 2014	Feb. 12, 2014	Oct. 31, 2013	Sep. 19, 2013	Apr. 30, 2013	Mar. 26, 2013	Dec. 13, 2012	Oct. 29, 2012	Apr. 28, 2008	Jan. 25, 2008	Jun. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2015 USD ($)	Jun. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares
Preferred stock
Carrying value														$ 13,968		$ 13,968	$ 10,468
Distribution of preferred dividends														$ 330
Forecast
Preferred stock
Distribution of preferred dividends															$ 439
Series AA
Preferred stock
Dividend rate (as a percent)																8.125%	8.125%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 25		$ 25	$ 25
Number of depositary shares (in shares) | shares														3,870,330		3,870,330	3,870,330
Carrying value														$ 97		$ 97	$ 97
Depositary shares, interest in corresponding series of preferred stock													0.001
Series E
Preferred stock
Dividend rate (as a percent)																8.40%	8.40%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 1,000		$ 1,000	$ 1,000
Number of depositary shares (in shares) | shares														121,254		121,254	121,254
Carrying value														$ 121		$ 121	$ 121
Depositary shares, interest in corresponding series of preferred stock												0.04
Series A
Preferred stock
Dividend rate (as a percent)																5.95%	5.95%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 1,000		$ 1,000	$ 1,000
Number of depositary shares (in shares) | shares														1,500,000		1,500,000	1,500,000
Carrying value														$ 1,500		$ 1,500	$ 1,500
Depositary shares, interest in corresponding series of preferred stock											0.04
Series B
Preferred stock
Dividend rate (as a percent)																5.90%	5.90%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 1,000		$ 1,000	$ 1,000
Number of depositary shares (in shares) | shares														750,000		750,000	750,000
Carrying value														$ 750		$ 750	$ 750
Depositary shares, interest in corresponding series of preferred stock										0.04
Series C
Preferred stock
Dividend rate (as a percent)																5.80%	5.80%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 25		$ 25	$ 25
Number of depositary shares (in shares) | shares														23,000,000		23,000,000	23,000,000
Carrying value														$ 575		$ 575	$ 575
Depositary shares, interest in corresponding series of preferred stock									0.001
Series D
Preferred stock
Dividend rate (as a percent)																5.35%	5.35%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 1,000		$ 1,000	$ 1,000
Number of depositary shares (in shares) | shares														1,250,000		1,250,000	1,250,000
Carrying value														$ 1,250		$ 1,250	$ 1,250
Depositary shares, interest in corresponding series of preferred stock								0.04
Series J
Preferred stock
Dividend rate (as a percent)																7.125%	7.125%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 25		$ 25	$ 25
Number of depositary shares (in shares) | shares														38,000,000		38,000,000	38,000,000
Carrying value														$ 950		$ 950	$ 950
Depositary shares, interest in corresponding series of preferred stock							0.001
Series K
Preferred stock
Dividend rate (as a percent)																6.875%	6.875%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 25		$ 25	$ 25
Number of depositary shares (in shares) | shares														59,800,000		59,800,000	59,800,000
Carrying value														$ 1,495		$ 1,495	$ 1,495
Depositary shares, interest in corresponding series of preferred stock						0.001
Series L
Preferred stock
Dividend rate (as a percent)																6.875%	6.875%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 25		$ 25	$ 25
Number of depositary shares (in shares) | shares														19,200,000		19,200,000	19,200,000
Carrying value														$ 480		$ 480	$ 480
Depositary shares, interest in corresponding series of preferred stock					0.001
Series M
Preferred stock
Dividend rate (as a percent)																6.30%	6.30%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 1,000		$ 1,000	$ 1,000
Number of depositary shares (in shares) | shares														1,750,000		1,750,000	1,750,000
Carrying value														$ 1,750		$ 1,750	$ 1,750
Depositary shares, interest in corresponding series of preferred stock				0.04
Series N
Preferred stock
Dividend rate (as a percent)																5.80%	5.80%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 1,000		$ 1,000	$ 1,000
Number of depositary shares (in shares) | shares														1,500,000		1,500,000	1,500,000
Carrying value														$ 1,500		$ 1,500	$ 1,500
Depositary shares, interest in corresponding series of preferred stock			0.04
Series O
Preferred stock
Dividend rate (as a percent)																5.875%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 1,000		$ 1,000
Number of depositary shares (in shares) | shares														1,500,000		1,500,000
Carrying value														$ 1,500		$ 1,500	0
Depositary shares, interest in corresponding series of preferred stock		0.04
Series P
Preferred stock
Dividend rate (as a percent)																5.95%
Redemption price per depositary share/ preference share (in dollars per share) | $ / shares														$ 1,000		$ 1,000
Number of depositary shares (in shares) | shares														2,000,000		2,000,000
Carrying value														$ 2,000		$ 2,000	$ 0
Depositary shares, interest in corresponding series of preferred stock	0.04