Quarterly Results (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	$ 14,832	$ 14,497	$ 13,979	$ 13,786	$ 13,648	$ 13,208	$ 12,219	$ 12,336	$ 57,094	$ 51,411	$ 50,601
Net income (loss) applicable to common shareholders, basic	1,460	(41)	(1,389)	(346)	(303)	(685)	(1,040)	634	(316)	(1,394)	1,500
Net income (loss) applicable to common shareholders, diluted	$ 1,460	$ (41)	$ (1,389)	$ (346)	$ (303)	$ (685)	$ (1,040)	$ 634	$ (316)	$ (1,394)	$ 1,500
Earnings per common share applicable to common shareholders - Basic (in dollars per share)	$ 5.57	$ (0.16)	$ (5.29)	$ (1.31)	$ (1.15)	$ (2.55)	$ (3.80)	$ 2.28	$ (1.20)	$ (5.14)	$ 5.09
Earnings per common share applicable to common shareholders - Diluted (in dollars per share)	$ 5.52	$ (0.16)	$ (5.29)	$ (1.31)	$ (1.15)	$ (2.55)	$ (3.80)	$ 2.25	$ (1.20)	$ (5.14)	$ 5.01
Accounting Standards Update 2018-12 | Cumulative effect of change in accounting principle
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues					$ 1	$ 0	$ (1)	$ (1)
Net income (loss) applicable to common shareholders, basic					7	9	2	4
Net income (loss) applicable to common shareholders, diluted					$ 7	$ 9	$ 2	$ 4
Earnings per common share applicable to common shareholders - Basic (in dollars per share)					$ 0.02	$ 0.03	$ 0.01	$ 0.01
Earnings per common share applicable to common shareholders - Diluted (in dollars per share)					$ 0.02	$ 0.03	$ 0.01	$ 0.01