Plan Assets Related to Pension and OPB Benefits by Level within the Fair Value Hierarchy (Detail) - USD ($) $ in Millions		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plan, Fair Value of Plan Assets		$ 3,432	[1]	$ 3,156	[2]
Defined Benefit Plan Accrued Income Threshold for Inclusion, Percent of Total Plan Assets		1.00%		1.00%
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		$ 1,743	[1]	$ 1,675	[2]
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		1,689	[1]	1,481	[2]
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1]	0	[2]
Money Market Funds [Member]
Defined Benefit Plan, Fair Value of Plan Assets		138	[1],[3]	112	[2],[4]
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		138	[1],[3]	112	[2],[4]
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1],[3]	0	[2],[4]
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1],[3]	0	[2],[4]
Pension Plan [Member]
Defined Benefit Plan, Fair Value of Plan Assets	[5]	3,288	[6]	3,016	[6]	$ 2,879
Pension Plan [Member] | Equity Securities [Member]
Defined Benefit Plan, Fair Value of Plan Assets		936	[1]	1,415	[2]
Pension Plan [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		936	[1]	1,415	[2]
Pension Plan [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1]	0	[2]
Pension Plan [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1]	0	[2]
Pension Plan [Member] | Future [Member]
Defined Benefit Plan, Fair Value of Plan Assets		(5)	[1]	(5)	[2]
Pension Plan [Member] | Future [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		(5)	[1]	0	[2]
Pension Plan [Member] | Future [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1]	5	[2]
Pension Plan [Member] | Future [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1]	0	[2]
Pension Plan [Member] | Fixed Income Securities [Member]
Defined Benefit Plan, Fair Value of Plan Assets		2,201	[1]	1,486	[2]
Pension Plan [Member] | Fixed Income Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		512	[1]	0	[2]
Pension Plan [Member] | Fixed Income Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		1,689	[1]	1,486	[2]
Pension Plan [Member] | Fixed Income Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1]	0	[2]
Pension Plan [Member] | Other Assets [Member]
Defined Benefit Plan, Fair Value of Plan Assets		9	[1]	6	[2]
Pension Plan [Member] | Other Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		9	[1]	6	[2]
Pension Plan [Member] | Other Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1]	0	[2]
Pension Plan [Member] | Other Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1]	0	[2]
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Fair Value of Plan Assets		164	[6]	157	[6]	$ 156
Other Postretirement Benefits Plan [Member] | Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		11	[1],[3]	16	[2],[4]
Other Postretirement Benefits Plan [Member] | Equity Funds [Member]
Defined Benefit Plan, Fair Value of Plan Assets		56	[1],[7]	47	[2],[8]
Other Postretirement Benefits Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		56	[1],[7]	47	[2],[8]
Other Postretirement Benefits Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1],[7]	0	[2],[8]
Other Postretirement Benefits Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1],[7]	0	[2],[8]
Other Postretirement Benefits Plan [Member] | Nontaxable Municipal Bonds [Member]
Defined Benefit Plan, Fair Value of Plan Assets		85	[1],[7]	82	[2],[8]
Other Postretirement Benefits Plan [Member] | Nontaxable Municipal Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		85	[1],[7]	82	[2],[8]
Other Postretirement Benefits Plan [Member] | Nontaxable Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1],[7]	0	[2],[8]
Other Postretirement Benefits Plan [Member] | Nontaxable Municipal Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1],[7]	0	[2],[8]
Other Postretirement Benefits Plan [Member] | Taxable Fixed Income Index Funds [Member]
Defined Benefit Plan, Fair Value of Plan Assets		12	[1],[7]	13	[2],[8]
Other Postretirement Benefits Plan [Member] | Taxable Fixed Income Index Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		12	[1],[7]	13	[2],[8]
Other Postretirement Benefits Plan [Member] | Taxable Fixed Income Index Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		0	[1],[7]	0	[2],[8]
Other Postretirement Benefits Plan [Member] | Taxable Fixed Income Index Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Fair Value of Plan Assets		$ 0	[1],[7]	$ 0	[2],[8]

[1] Fair value measurements do not include pension benefits accrued income amounting to less than 0.7% of total plan assets.

[2] Fair value measurements do not include pension benefits accrued income amounting to less than 0.6% of total plan assets.

[3] Includes $11 million for other postretirement benefit plans.

[4] Includes $16 million for other postretirement benefit plans.

[5] Employer contributions represent the benefits that were paid to nonqualified plan participants. Unfunded nonqualified supplemental pension plans are not funded through plan assets.

[6] Includes $1 million and $2 million of the Company's common stock acquired by the asset manager and held as part of the equity portfolio for pension benefits at December 31, 2017 and 2016, respectively. During both 2017 and 2016, there was no SunTrust common stock held in the other postretirement benefit plans.

[7] Relates exclusively to other postretirement benefit plans.

[8] Relates exclusively to other postretirement benefit plans.