Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Preferred Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]
Balance at beginning of period at Dec. 31, 2018	$ 11,659		$ 0	$ 0	$ 8,058	$ (1,066)	$ 4,667
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	271						271
Other comprehensive income (loss)	42					42
Stock based compensation	11				11
Other	1						1
Balance at end of period at Mar. 31, 2019	11,984		0	0	8,069	(1,024)	4,939
Balance at beginning of period at Dec. 31, 2018	11,659		0	0	8,058	(1,066)	4,667
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	674
Other comprehensive income (loss)	32
Balance at end of period at Jun. 30, 2019	12,385		0	0	8,077	(1,034)	5,342
Balance at beginning of period at Mar. 31, 2019	11,984		0	0	8,069	(1,024)	4,939
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	403						403
Other comprehensive income (loss)	(10)					(10)
Stock based compensation	8				8
Balance at end of period at Jun. 30, 2019	12,385		0	0	8,077	(1,034)	5,342
Balance at beginning of period at Dec. 31, 2019	12,726	$ (643)	0	0	8,101	(1,119)	5,744
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	167						167
Other comprehensive income (loss)	(543)					(543)
Stock based compensation	9				9
Dividends paid (Note 11)	(400)						(400)
Balance at end of period at Mar. 31, 2020	11,316		0	0	8,110	(1,662)	4,868
Balance at beginning of period at Dec. 31, 2019	12,726	$ (643)	0	0	8,101	(1,119)	5,744
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	340
Other comprehensive income (loss)	(544)
Balance at end of period at Jun. 30, 2020	11,053		0	0	8,120	(1,663)	4,596
Balance at beginning of period at Mar. 31, 2020	11,316		0	0	8,110	(1,662)	4,868
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	173						173
Other comprehensive income (loss)	(1)					(1)
Stock based compensation	10				10
Dividends paid (Note 11)	(400)						(400)
Dividends declared on preferred stock (Note 11)	(45)						(45)
Balance at end of period at Jun. 30, 2020	$ 11,053		$ 0	$ 0	$ 8,120	$ (1,663)	$ 4,596