Preferred Stock (Details)		1 Months Ended	6 Months Ended	12 Months Ended
	May 29, 2016 USD ($) $ / shares Rate shares	Jun. 30, 2016 USD ($) $ / shares shares	Jun. 30, 2016 USD ($) $ / shares Rate shares	Dec. 31, 2015 USD ($) $ / shares Rate
Class of Stock [Line Items]
Preferred Stock, Value, Issued | $		$ 39,000,000	$ 39,000,000	$ 39,000,000
Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Outstanding | shares		390,000	390,000
Preferred Stock, Par or Stated Value Per Share		$ 100	$ 100
Preferred Stock, Redemption Amount | $		$ 40,100,000	$ 40,100,000
Preferred Stock, Redemption Date		Aug. 10, 2016
Preferred Stock 3 Point 80 [Member]
Class of Stock [Line Items]
Preferred Stock, Value, Issued | $		$ 10,000,000	$ 10,000,000	$ 10,000,000
Preferred Stock, Par or Stated Value Per Share		$ 100.00	$ 100.00	$ 100.00
Preferred Stock, Dividend Rate, Percentage | Rate			3.80%	3.80%
Preferred Stock, Redemption Price Per Share		103.70	$ 103.70
Accrued and Unpaid Preferred Dividends		0.75	0.75
Preferred Stock, Redemption Price Per Share, Including Accrued and Unpaid Dividends		$ 104.45	$ 104.45
Preferred Stock 4 Point 20 [Member]
Class of Stock [Line Items]
Preferred Stock, Value, Issued | $		$ 7,000,000	$ 7,000,000	$ 7,000,000
Preferred Stock, Par or Stated Value Per Share		$ 100.00	$ 100.00	$ 100.00
Preferred Stock, Dividend Rate, Percentage | Rate			4.20%	4.20%
Preferred Stock, Redemption Price Per Share		102.00	$ 102.00
Accrued and Unpaid Preferred Dividends		0.83	0.83
Preferred Stock, Redemption Price Per Share, Including Accrued and Unpaid Dividends		$ 102.83	$ 102.83
Preferred Stock 4 Point 35 [Member]
Class of Stock [Line Items]
Preferred Stock, Value, Issued | $		$ 12,000,000	$ 12,000,000	$ 12,000,000
Preferred Stock, Par or Stated Value Per Share		$ 100.00	$ 100.00	$ 100.00
Preferred Stock, Dividend Rate, Percentage | Rate			4.35%	4.35%
Preferred Stock, Redemption Price Per Share		101.00	$ 101.00
Accrued and Unpaid Preferred Dividends		0.86	0.86
Preferred Stock, Redemption Price Per Share, Including Accrued and Unpaid Dividends		$ 101.86	$ 101.86
Preferred Stock 4 Point 50 [Member]
Class of Stock [Line Items]
Preferred Stock, Value, Issued | $		$ 10,000,000	$ 10,000,000	$ 10,000,000
Preferred Stock, Par or Stated Value Per Share		$ 100.00	$ 100.00	$ 100.00
Preferred Stock, Dividend Rate, Percentage | Rate			4.50%	4.50%
Preferred Stock, Redemption Price Per Share		101.00	$ 101.00
Accrued and Unpaid Preferred Dividends		0.89	0.89
Preferred Stock, Redemption Price Per Share, Including Accrued and Unpaid Dividends		101.89	$ 101.89
7.25% Mandatory Convertible Preferred Stock, Series A [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage | Rate	7.25%		7.25%
Preferred Stock, Purchase Agreement, Proceeds | $	$ 750,000,000
Applicable Market Value, Maximum	$ 34.38
Applicable Market Value, Minimum	$ 28.65
Conversion Rate, if Applicable Market Value is equal to or greater than $34.38	29.0855
Conversion Rate, if Applicable Market Value is less than or equal to $28.65	34.9026
Conversion Rate, Numerator | $	$ 1,000.00
Conversion Rate, Voluntary	29.0855
Preferred Shares To Be Issued, Stock Purchase Agreement, Series A Preferred Stock | shares	750,000
Preferred Stock, Liquidation Preference Per Share		$ 1,000	$ 1,000
Minimum [Member] | 7.25% Mandatory Convertible Preferred Stock, Series A [Member]
Class of Stock [Line Items]
Applicable Market Value Less Than Maximum Greater Than Minimum	$ 28.65
Maximum [Member] | 7.25% Mandatory Convertible Preferred Stock, Series A [Member]
Class of Stock [Line Items]
Applicable Market Value Less Than Maximum Greater Than Minimum	$ 34.38