Stockholders' Equity (Details)				1 Months Ended	8 Months Ended	12 Months Ended
	Sep. 19, 2018 $ / shares shares	Sep. 15, 2016 $ / shares shares	Jun. 15, 2015 $ / shares shares	Nov. 30, 2008 USD ($) $ / shares	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) shares	Feb. 05, 2019 USD ($)	Nov. 21, 2018 shares	Sep. 18, 2018 USD ($)	Apr. 24, 2018 USD ($)	Jul. 25, 2017 USD ($)	Aug. 28, 2015 USD ($)
Stockholders' Equity Note [Abstract]
Subsidiary equity balance					$ 3,800,000,000	$ 3,800,000,000
Class of Stock [Line Items]
Purchase of stock, value						$ 537,000		$ 1,248,000
Series C Preferred Stock
Class of Stock [Line Items]
Depositary shares issued (in shares) | shares			2,600,000
Preferred Stock, Dividend Rate, Percentage			6.125%			6.125%
Liquidation preference on depositary shares (in usd per share) | $ / shares			$ 1,000
Preferred Stock, Redemption Terms			Jun. 15, 2020
Redemption Price On Depositary Shares | $ / shares			$ 1,000
Depositary share value (in usd per share) | $ / shares			$ 25
Stock repurchase program authorized amount														$ 10,000,000
Remaining authorized repurchase amount					10,000,000	$ 10,000,000
Depository share ratio			0.025
Series D Preferred Stock
Class of Stock [Line Items]
Depositary shares issued (in shares) | shares		4,000,000.0
Preferred Stock, Dividend Rate, Percentage		5.375%				5.375%
Liquidation preference on depositary shares (in usd per share) | $ / shares		$ 1,000
Preferred Stock, Redemption Terms		Sep. 15, 2021
Redemption Price On Depositary Shares | $ / shares		$ 1,000
Depositary share value (in usd per share) | $ / shares		$ 25
Stock repurchase program authorized amount													$ 15,000,000
Purchase of stock, value						$ 537,057
Stock Repurchased During Period, Shares | shares						22,000
Remaining authorized repurchase amount					14,000,000	$ 14,000,000
Depository share ratio		0.025
Series E Preferred Stock
Class of Stock [Line Items]
Depositary shares issued (in shares) | shares	4,000,000.0
Preferred Stock, Dividend Rate, Percentage	5.875%					5.875%
Liquidation preference on depositary shares (in usd per share) | $ / shares	$ 1,000
Preferred Stock, Redemption Terms	Dec. 15, 2023
Redemption Price On Depositary Shares | $ / shares	$ 1,000
Depositary share value (in usd per share) | $ / shares	$ 25
Depository share ratio	0.025
Common Stock
Class of Stock [Line Items]
Stock repurchase program authorized amount											$ 200,000,000	$ 100,000,000
Purchase of stock, value					100,000,000	$ 51,000,000
Remaining authorized repurchase amount					111,000,000	$ 111,000,000
Warrants to purchase shares of common stock (in shares)				$ 4,000,000.0
Term of warrants				10 years
Exercise price of warrants (in usd per share) | $ / shares				$ 19.77
Class of Warrant or Right, Outstanding | shares										12,507
Unexercised Warrants, Expired Shares | shares										12,507
Treasury stock shares acquired (in shares) | shares						9,500,000	1,600,000
Treasury stock carrying basis					240,000,000	$ 240,000,000	$ 37,000,000
Treasury stock acquired average cost per share (in usd per share) | $ / shares						$ 25.29	$ 23.59
Repurchased amount for minimum tax withholding settlement						$ 7,000,000	$ 9,000,000
Repurchased shares for minimum tax withholding settlements (in shares) | shares						292,070	370,416
Minimum tax withholding settlement average cost per share (in usd per share) | $ / shares						$ 24.47	$ 25.08
Treasury Stock
Class of Stock [Line Items]
Treasury stock shares acquired (in shares) | shares						1,400,000
Treasury stock carrying basis					$ 33,000,000	$ 33,000,000
Treasury stock acquired average cost per share (in usd per share) | $ / shares						$ 24.38
Treasury Stock, Shares, Retired | shares						8,100,000
Treasury Stock, Retired, Cost Method, Amount						$ 206,000,000
Subsequent Event | Common Stock
Class of Stock [Line Items]
Stock repurchase program authorized amount									$ 100,000,000
Remaining authorized repurchase amount									$ 211,000,000
Common Stock
Class of Stock [Line Items]
Purchase of stock, value						$ 0		$ 0
Stock Repurchased During Period, Shares | shares						0		0
Shares from Warrant Exercises | shares						1,116,000