Equity (Terms of Outstanding Preferred Stock) (Details)			4 Months Ended		7 Months Ended	9 Months Ended		12 Months Ended
		Nov. 01, 2016 shares	May 07, 2013 shares	Apr. 24, 2012 shares	Jul. 27, 2011 shares	Oct. 09, 2012 shares	Sep. 21, 2012 shares	Dec. 31, 2017 voting_right $ / shares	May 04, 2015 shares
Series B Preferred Stock
Debt Instrument [Line Items]
Preferred Stock, Dividend Rate, Per-Dollar-Amount | $ / shares								$ 1.8
Preferred stock, voting rights | voting_right								8
Series O Preferred Stock
Debt Instrument [Line Items]
Preferred Stock, Dividend Rate, Percentage					6.75%
Depositary Shares					1,000,000
Interest In Preferred Stock					1.00%
Series P Preferred Stock
Debt Instrument [Line Items]
Preferred Stock, Dividend Rate, Percentage				6.125%
Depositary Shares				60,000,000
Interest In Preferred Stock				0.025%
Series Q Preferred Stock
Debt Instrument [Line Items]
Preferred Stock, Dividend Rate, Percentage						5.375%	5.375%
Depositary Shares						1,200,000	18,000,000
Interest In Preferred Stock						0.025%	0.025%
Series R Preferred Stock
Debt Instrument [Line Items]
Preferred Stock, Dividend Rate, Percentage			4.85%
Depositary Shares			500,000
Interest In Preferred Stock			1.00%
Series S Preferred Stock
Debt Instrument [Line Items]
Preferred Stock, Dividend Rate, Percentage		5.00%
Depositary Shares		525,000
Interest In Preferred Stock		1.00%
Series K Preferred Stock
Debt Instrument [Line Items]
Depositary Shares	[1]								500,000
3-month LIBOR | Series O Preferred Stock
Debt Instrument [Line Items]
Basis spread on variable rate - LIBOR Plus					3.678%
3-month LIBOR | Series P Preferred Stock
Debt Instrument [Line Items]
Basis spread on variable rate - LIBOR Plus				4.0675%
3-month LIBOR | Series R Preferred Stock
Debt Instrument [Line Items]
Basis spread on variable rate - LIBOR Plus			3.04%
3-month LIBOR | Series S Preferred Stock
Debt Instrument [Line Items]
Basis spread on variable rate - LIBOR Plus		3.30%

[1] On May 4, 2015, we redeemed all 50,000 shares of our Series K preferred stock, as well as all 500,000 Depositary Shares representing fractional interests in such shares, resulting in net outflow of $500 million.