Benefit Plans - Summary of the Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net periodic pension cost:
Service cost		$ 612	$ 518	$ 214
Interest cost		319	313	233
Estimated return on plan assets		(998)	(866)	(480)
Net amortization and other		35	76	111
Net periodic (benefit) cost		(32)	41	78
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Net actuarial loss (gain)		(1,012)	(244)	34
Net amortization		(35)	(77)	(110)
Net amount recognized in OCI		(1,047)	(321)	(76)
Total net periodic pension costs (income) recognized in total comprehensive income, pre-tax		$ (1,079)	$ (280)	$ 2
Weighted average assumptions used to determine net periodic pension cost:
Discount rate		2.94%	3.45%	4.43%
Expected long-term rate of return on plan assets		6.70%	6.90%	7.00%
Assumed long-term rate of annual compensation increases		4.50%	4.50%	4.50%
SunTrust Banks Inc.
Weighted average assumptions used to determine net periodic pension cost:
Discount rate	3.22%
Expected long-term rate of return on plan assets	6.90%