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, 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: $72.52/share	(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: $72.52/share	(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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	428				387	41
Dividends declared:
Preferred stock: $72.52/share	(8)				(8)
Common stock: $0.48/share	(157)				(157)
Issuance of common stock	0			6			(6)
Restricted stock compensation	12			12
Balance at end of period at Dec. 31, 2019	$ 4,883	$ 107	$ 3	$ 4,067	$ 798	$ (65)	$ (27)