Shareholders' Equity (Preferred Shares) (Narrative) (Details)						3 Months Ended		6 Months Ended
	Jul. 10, 2020	Jun. 17, 2020 USD ($) $ / shares shares	Jun. 27, 2019	Mar. 28, 2019	Mar. 11, 2019 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) $ / shares	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) item $ / shares	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Class of Stock [Line Items]
Number of quarterly dividends in arrearage before preferred shareholders can elect additional board members | item								6
Number of additional board members the preferred shareholders can elect in the case of an excess arrearage of quarterly dividends | item								2
Amount of preferred dividends in arrears								$ 0
Affirmative vote of outstanding shares of a series of Preferred Shares required for any material and adverse amendment to the terms of series, percent								66.67%
Affirmative vote of outstanding shares of all Preferred Shares, voting as a single class, required to issue shares ranking senior to Preferred Shares, percent								66.67%
Redemption price per share | $ / shares						$ 25.00		$ 25.00
Gross proceeds from issuance of preferred stock								$ 549,170,000	$ 276,723,000
EITF D-42 allocations						$ 15,069,000	$ 8,861,000	15,069,000	17,394,000
Liquidation value (at par)						4,135,000,000		$ 4,135,000,000		$ 4,065,000,000
Series H Preferred Stock [Member]
Class of Stock [Line Items]
Redemption price per share | $ / shares					$ 25.00
Shares issued | shares					11,400,000
Preferred shares per depositary share | shares					0.001
Gross proceeds from issuance of preferred stock					$ 285,000,000.0
Original issuance costs on preferred shares redeemed during the period					$ 8,300,000
Dividend rate percentage					5.60%			5.60%
Liquidation value (at par)						285,000,000		$ 285,000,000		285,000,000
Series Y Preferred Stock [Member]
Class of Stock [Line Items]
Dividend rate percentage				6.375%
EITF D-42 allocations									8,500,000
Series Z Preferred Stock [Member]
Class of Stock [Line Items]
Dividend rate percentage			6.00%
EITF D-42 allocations							$ 8,900,000		$ 8,900,000
Series L Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued | shares		22,600,000
Preferred shares per depositary share | shares		0.001
Shares issued, price per share | $ / shares		$ 25.00
Gross proceeds from issuance of preferred stock		$ 565,000,000.0
Original issuance costs on preferred shares redeemed during the period		$ 15,800,000
Dividend rate percentage		4.625%						4.625%
Liquidation value (at par)						565,000,000		$ 565,000,000
Series V Preferred Stock [Member]
Class of Stock [Line Items]
Dividend rate percentage								5.375%
EITF D-42 allocations						15,100,000		$ 15,100,000
Liquidation value (at par)						$ 495,000,000.0		$ 495,000,000.0		$ 495,000,000
Subsequent Event [Member] | Series V Preferred Stock [Member]
Class of Stock [Line Items]
Dividend rate percentage	5.375%