Shareholders' Equity - Schedule of Preferred Stock (Details)	Dec. 31, 2018 USD ($) $ / shares shares
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, amount outstanding | $	$ 525,000,000
Preferred stock, shares authorized (in shares) | shares	21,000
Preferred stock, shares outstanding (in shares) | shares	21,000
Preferred stock, par value (in usd per share)	$ 1
Preferred stock, liquidation preference, value | $	$ 25,000
Depository Shares, Series D [Member]
Class of Stock [Line Items]
Depository receipt ratio	0.04
Preferred stock, liquidation preference (in usd per share)	$ 1,000
Dividend payable per share (in usd per share)	$ 50.00
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, amount outstanding | $	$ 500,000,000
Preferred stock, shares authorized (in shares) | shares	500,000
Preferred stock, shares outstanding (in shares) | shares	500,000
Preferred stock, par value (in usd per share)	$ 1
Preferred stock, liquidation preference, value | $	$ 1,000
Depository Shares, Series E [Member]
Class of Stock [Line Items]
Depository receipt ratio	25,000.000
Preferred stock, liquidation preference (in usd per share)	$ 25
Dividend payable per share (in usd per share)	$ 1.531252
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, amount outstanding | $	$ 425,000,000
Preferred stock, shares authorized (in shares) | shares	425,000
Preferred stock, shares outstanding (in shares) | shares	425,000
Preferred stock, par value (in usd per share)	$ 1
Preferred stock, liquidation preference, value | $	$ 1,000
Depository Shares, Series F [Member]
Class of Stock [Line Items]
Depository receipt ratio	25,000.000
Preferred stock, liquidation preference (in usd per share)	$ 25
Dividend payable per share (in usd per share)	$ 0.529688