Contingencies - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2018 USD ($)
Document Period End Date	Sep. 30, 2018
Minimum [Member]
Aggregate range of reasonably possible losses on legal matters in excess of the accrued liability	$ 0
Maximum [Member]
Aggregate range of reasonably possible losses on legal matters in excess of the accrued liability	160,000,000
LR Trust v. SunTrust Banks, Inc., et al. [Member]
Loss Contingency, Damages Awarded, Value	585,000
Cash payment for litigation [Member] | Potential Mortgage Servicing Settlement and Claims [Member]
Loss Contingency, Damages Awarded, Value	50,000,000
Consumer relief obligation [Member] | Potential Mortgage Servicing Settlement and Claims [Member]
Loss Contingency, Damages Awarded, Value	$ 500,000,000