EARNINGS PER COMMON SHARE AND DIVIDEND PER SHARE - Dividend Per Share (Details)	1 Months Ended			2 Months Ended			6 Months Ended
	Jun. 30, 2019 $ / shares	Mar. 31, 2019 $ / shares	Mar. 31, 2019 $ / shares	May 31, 2019 $ / shares	Feb. 28, 2019 $ / shares	Feb. 28, 2019 $ / shares	Jun. 30, 2019 $ / shares	Jun. 30, 2019 $ / shares
Common shares
Dividends Payable [Line Items]
Common stock, dividends, per share, declared (in dollars per share)							$ 0.73800
Preference Shares, Series A | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							0.34375
Preference Shares, Series B | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							0.21340
Preference Shares, Series C | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)	$ 0.25647	$ 0.25395		$ 0.25395	$ 0.25459		0.25647
Preference Shares, Series D | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							0.27875
Preference Shares, Series F | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							0.29306
Preference Shares, Series H | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							0.27350
Preference Shares, Series J | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)								$ 0.30540
Preference Shares, Series L | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)								0.30993
Preference Shares, Series N | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							0.31788
Preference Shares, Series P | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)		0.27369			0.25000		0.27369
Preference Shares, Series R | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)	$ 0.25456			$ 0.25000			0.25456
Preference Shares, Series 1 | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)								0.37182
Preference Shares, Series 3 | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							0.25000
Preference Shares, Series 5 | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)			$ 0.33596			$ 0.27500		$ 0.33596
Preference Shares, Series 7 | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)		$ 0.27806			$ 0.27500		0.27806
Preference Shares, Series 9 | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							0.27500
Preference Shares, Series 11 | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							0.27500
Preference Shares, Series 13 | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							0.27500
Preference Shares, Series 15 | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							0.27500
Preference Shares, Series 17 | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							0.32188
Preference Shares, Series 19 | Preferred share investment
Dividends Payable [Line Items]
Dividend per share (in dollars per share)							$ 0.30625