Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Balance at beginning of period at Dec. 31, 2015	$ 2,096	$ 107	$ 2	$ 1,808	$ 243	$ (51)	$ (13)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	161				171	(10)
Dividends declared:
Preferred stock	(8)				(8)
Common stock: $0.48/share	(102)				(102)
Issuance of common stock	12			14			(2)
Issuance of common stock – acquisitions	404			404
Restricted stock compensation	7			7
Tax benefit of stock-based compensation	2			2
Balance at end of period at Dec. 31, 2016	2,572	107	2	2,235	304	(61)	(15)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	192				199	(7)
Dividends declared:
Preferred stock	(8)				(8)
Common stock: $0.48/share	(142)				(142)
Issuance of common stock	3			7			(4)
Issuance of common stock – acquisitions	1,783		1	1,782
Assumption of warrant due to acquisition	1			1
Restricted stock compensation	8			8
Reclassification due to tax reform	0				15	(15)
Balance at end of period at Dec. 31, 2017	4,409	107	3	4,033	368	(83)	(19)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	350				373	(23)
Dividends declared:
Preferred stock	(8)				(8)
Common stock: $0.48/share	(157)				(157)
Issuance of common stock	4			6			(2)
Restricted stock compensation	10			10
Balance at end of period at Dec. 31, 2018	$ 4,608	$ 107	$ 3	$ 4,049	$ 576	$ (106)	$ (21)