SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF PARENT - STATEMENT OF OPERATIONS (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
Condensed Income Statements, Captions [Line Items]
Interest income									$ 96	$ 87	$ 85
Interest expense									(1,081)	(1,077)	(886)
Other (expense) income, net									(48)	77	58
Income tax benefit									(249)	(315)	49
Net of income tax									2,255	1,999	938
Net income	$ 432	$ 421	$ 2,305	$ 947	$ 500	$ 909	$ 435	$ 518	$ 4,105	$ 2,362	$ 1,126
Earnings attributable to common shares	$ 414	$ 351	$ 2,239	$ 760	$ 447	$ 813	$ 354	$ 441
Basic earnings per common share (in shares)									$ 12.93	$ 7.40	$ 3.45
Weighted-average number of shares outstanding, basic (in shares)	289,000	289,500	293,100	292,800	284,600	277,400	275,000	274,700	291,077	277,904	268,072
Diluted earnings per common share (in dollars per share)									$ 12.88	$ 7.29	$ 3.42
Weighted-average number of shares outstanding, diluted (in shares)	290,200	290,600	294,200	313,900	288,800	295,800	279,600	277,200	292,252	282,033	269,852
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Interest income									$ 4	$ 3	$ 14
Interest expense									(495)	(521)	(495)
Operating expenses									(86)	(124)	(82)
Other (expense) income, net									(38)	59	(16)
Income tax benefit									176	163	154
Net of income tax									(439)	(420)	(425)
Equity in earnings of subsidiaries, net of income taxes									4,371	2,617	1,474
Net income									3,932	2,197	1,049
Preferred dividends									(168)	(142)	(125)
Earnings attributable to common shares									$ 3,764	$ 2,055	$ 924
Basic earnings per common share (in shares)									$ 12.93	$ 7.40	$ 3.45
Weighted-average number of shares outstanding, basic (in shares)									291,077	277,904	268,072
Diluted earnings per common share (in dollars per share)									$ 12.88	$ 7.29	$ 3.42
Weighted-average number of shares outstanding, diluted (in shares)									292,252	282,033	269,852