Earnings per Common Share (Schedule of Basic and Diluted Earnings per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net income from continuing operations	$ 687	$ 476	$ 242	$ (319)	$ 381	$ 381	$ 584	$ 375	$ 1,086	$ 1,721	$ 1,263
Loss from discontinued operations, net of tax	0	0	(1)	0	(3)	0	(2)	(1)	(1)	(6)	0
Net income	$ 687	$ 476	$ 241	$ (319)	$ 378	$ 381	$ 582	$ 374	$ 1,085	$ 1,715	$ 1,263
Basic weighted-average common shares outstanding									375,629	393,234	425,165
Diluted weighted-average common shares outstanding									377,101	395,395	427,680
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									800	0	0
Earnings Per Share, Basic [Abstract]
Net (loss) income from continuing operations, basic earnings per common share	$ 1.83	$ 1.27	$ 0.65	$ (0.85)	$ 1.00	$ 0.98	$ 1.47	$ 0.93	$ 2.89	$ 4.38	$ 2.97
Loss from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share									0	(0.02)	0
Net income, basic earnings per common share	1.83	1.27	0.64	(0.85)	0.99	0.97	1.46	0.93	2.89	4.36	2.97
Earnings Per Share, Diluted [Abstract]
Net (loss) income from continuing operations, diluted earnings per common share	1.82	1.26	0.64	(0.85)	0.99	0.97	1.46	0.92	2.88	4.35	2.95
Loss from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share									0	(0.02)	0
Net (loss) income, diluted earnings per common share	$ 1.82	$ 1.26	$ 0.64	$ (0.85)	$ 0.99	$ 0.97	$ 1.46	$ 0.92	$ 2.88	$ 4.34	$ 2.95