Premises and Equipment - Premises and Equipment and Estimated Useful Lives (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Premises and Equipment, Net, by Type
Premises and equipment, gross		$ 732
Total	$ 811
Less accumulated depreciation	(395)
Less accumulated depreciation		(342)
Premises and equipment, net	$ 416
Premises and equipment, net		390
Range (Weighted Average)
Premises and Equipment, Net, by Type
Estimated useful lives	3 years
Maximum
Premises and Equipment, Net, by Type
Estimated useful lives	30 years
Land Improvements [Member] | Range (Weighted Average)
Premises and Equipment, Net, by Type
Estimated useful lives	5 years
Land Improvements [Member] | Maximum
Premises and Equipment, Net, by Type
Estimated useful lives	10 years
Land
Premises and Equipment, Net, by Type
Premises and equipment, gross		74
Computer hardware and software
Premises and Equipment, Net, by Type
Premises and equipment, gross		329
Computer hardware and software | Range (Weighted Average)
Premises and Equipment, Net, by Type
Estimated useful lives	3 years
Computer hardware and software | Maximum
Premises and Equipment, Net, by Type
Estimated useful lives	7 years
Office buildings and improvements
Premises and Equipment, Net, by Type
Premises and equipment, gross		185
Office buildings and improvements | Range (Weighted Average)
Premises and Equipment, Net, by Type
Estimated useful lives	15 years
Office buildings and improvements | Maximum
Premises and Equipment, Net, by Type
Estimated useful lives	31 years 6 months
Furniture, fixtures and equipment
Premises and Equipment, Net, by Type
Premises and equipment, gross		57
Furniture, fixtures and equipment | Range (Weighted Average)
Premises and Equipment, Net, by Type
Estimated useful lives	5 years
Furniture, fixtures and equipment | Maximum
Premises and Equipment, Net, by Type
Estimated useful lives	7 years
Leased equipment
Premises and Equipment, Net, by Type
Premises and equipment, gross		40
Leased equipment | Range (Weighted Average)
Premises and Equipment, Net, by Type
Estimated useful lives	3 years
Leased equipment | Maximum
Premises and Equipment, Net, by Type
Estimated useful lives	10 years
Leasehold improvements
Premises and Equipment, Net, by Type
Premises and equipment, gross		10
Fixed assets in progress
Premises and Equipment, Net, by Type
Premises and equipment, gross		37
Right-of-use asset
Premises and Equipment, Net, by Type
Premises and equipment, gross		$ 0
Land
Premises and Equipment, Net, by Type
Premises and equipment, gross	$ 73
Computer hardware and software
Premises and Equipment, Net, by Type
Premises and equipment, gross	372
Office buildings and improvements
Premises and Equipment, Net, by Type
Premises and equipment, gross	191
Furniture, fixtures and equipment
Premises and Equipment, Net, by Type
Premises and equipment, gross	68
Leased equipment
Premises and Equipment, Net, by Type
Finance lease, right-of-use asset, before accumulated amortization	36
Leasehold improvements
Premises and Equipment, Net, by Type
Finance lease, right-of-use asset, before accumulated amortization	9
Fixed assets in progress
Premises and Equipment, Net, by Type
Premises and equipment, gross	40
Right-of-use asset
Premises and Equipment, Net, by Type
Finance lease, right-of-use asset, before accumulated amortization	$ 22