Intangible Assets - Schedule of Intangible Assets (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets
Gross Carrying Amount	$ 270	$ 273
Accumulated Amortization	(153)	(134)
Net Carrying Amount	117	139
Core deposit intangibles
Finite-Lived Intangible Assets
Gross Carrying Amount	229	229
Accumulated Amortization	(135)	(116)
Net Carrying Amount	94	113
Customer relationships
Finite-Lived Intangible Assets
Gross Carrying Amount	24	24
Accumulated Amortization	(6)	(5)
Net Carrying Amount	18	19
Operating leases
Finite-Lived Intangible Assets
Gross Carrying Amount	14	17
Accumulated Amortization	(11)	(12)
Net Carrying Amount	3	5
Other
Finite-Lived Intangible Assets
Gross Carrying Amount	3	3
Accumulated Amortization	(1)	(1)
Net Carrying Amount	$ 2	$ 2