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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Income Statements, Captions [Line Items]
Interest income									$ 87	$ 85	$ 24
Interest expense									(1,077)	(886)	(622)
Other (expense) income, net									77	58	220
Income tax benefit									(315)	49	(938)
Net of income tax									1,999	938	382
Net income	$ 500	$ 909	$ 435	$ 518	$ 964	$ 334	$ (530)	$ 358	2,362	1,126	351
Mandatory convertible preferred stock dividends									$ (142)	$ (125)	$ 0
Earnings attributable to common shares	$ 447	$ 813	$ 354	$ 441	$ 864	$ 274	$ (561)	$ 347
Basic earnings per common share (in shares)	$ 0.21	$ 0.89	$ 0.26	$ (0.19)	$ 0.15	$ 0.17	$ 0.18	$ 0.08	$ 7.40	$ 3.45	$ 1.02
Weighted-average number of shares outstanding, basic (in shares)	284,600	277,400	275,000	274,700	274,300	273,900	265,800	257,900	277,904	268,072	251,545
Diluted earnings per common share (in dollars per share)	$ 0.21	$ 0.84	$ 0.25	$ (0.19)	$ 0.14	$ 0.17	$ 0.18	$ 0.08	$ 7.29	$ 3.42	$ 1.01
Weighted-average number of shares outstanding, diluted (in shares)	288,800	295,800	279,600	277,200	296,400	275,900	265,800	259,500	282,033	269,852	252,300
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Interest income									$ 3	$ 14	$ 0
Interest expense									(521)	(495)	(293)
Operating expenses									(124)	(82)	(80)
Other (expense) income, net									59	(16)	100
Income tax benefit									163	154	33
Net of income tax									(420)	(425)	(240)
Equity in earnings of subsidiaries, net of income taxes									2,617	1,474	496
Net income									2,197	1,049	256
Mandatory convertible preferred stock dividends									(142)	(125)	0
Earnings attributable to common shares									$ 2,055	$ 924	$ 256
Basic earnings per common share (in shares)									$ 7.40	$ 3.45	$ 1.02
Weighted-average number of shares outstanding, basic (in shares)									277,904	268,072	251,545
Diluted earnings per common share (in dollars per share)									$ 7.29	$ 3.42	$ 1.01
Weighted-average number of shares outstanding, diluted (in shares)									282,033	269,852	252,300