Employee Benefits - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2009 benefit_plan
Defined Benefit Plan Disclosure [Line Items]
Pre-tax AOCI not yet recognized as net pension cost	$ 550	$ 593
Pre-tax accumulated other comprehensive loss expected to be recognized as net pension cost	17
Accumulated benefit obligation for all pension plans	$ 1,300	$ 1,100
Percentage increase or decrease in expected return on plan assets	0.25%
Estimated increase or decrease in net pension cost	$ 3
Percentage increase or decrease in assumed discount rate	0.25%
Estimated change in net pension cost due to discount rate	$ 1
Maximum limit for vary of market related value	10.00%
Expected return on plan assets	6.00%	6.25%	7.25%
Expected return on plan assets on estimating 2013 pension cost	6.00%
Discount rates to determine APBO	3.75%	4.00%
Employees minimum contribution to saving plan	1.00%
Employees maximum contribution to saving plan	100.00%
Employer contribution to saving plan	6.00%
Employee contribution to savings plan	10.00%
Increase in employee contribution to savings plan	1.00%
Profit sharing contribution, service period	1 year
Profit sharing allocation	2.50%	2.00%	2.00%
Total expenses associated with saving plan	$ 94	$ 79	$ 73
Initial Default Percentage [Member]
Defined Benefit Plan Disclosure [Line Items]
Employee contribution to savings plan	2.00%
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2017	$ 114
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2018	108
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2019	114
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2020	95
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2021	91
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2022 through 2026	422
Accumulated benefit obligation for all pension plans	1,338	1,136
Defined benefit plan, net periodic benefit cost expected in next fiscal year	5
Defined benefit plan, net periodic benefit cost expected	$ 21	$ 26	$ 19
Expected return on plan assets	6.00%	6.25%	7.25%
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax AOCI not yet recognized as net pension cost	$ (11)	$ (8)
Pre-tax accumulated other comprehensive loss expected to be recognized as net pension cost	1
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2017	5
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2018	5
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2019	5
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2020	5
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2021	5
Benefits expected to be paid from all funded and unfunded pension plans/other postretirement plans in 2022 through 2026	23
Defined benefit plan, net periodic benefit cost expected	$ 0	$ 0	$ (1)
Expected return on plan assets	4.50%	4.50%	5.25%
Age of employees under condition one	55 years
Period of service under condition one	5 years
Age of employees under condition two	50 years
Period of service under condition two	15 years
Minimum period of service at the time of termination hired before 2001	15 years
Other Postretirement Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, net periodic benefit cost expected in next fiscal year	$ 1
Defined benefit plan, net periodic benefit cost expected		$ 1
First Niagara Bank, N.A. [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of plans | benefit_plan				2