Deposits - Scheduled Maturity of Total Time Deposits (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Time Deposits [Line Items]
1 Year or Less	$ 1,692.5
Over 1 Year to 2 Years	196.6
Over 2 Years to 3 Years	7.4
Over 3 Years to 4 Years	3.8
Over 4 Years to 5 Years	4.2
Over 5 Years	0.9
Total	1,905.4	$ 1,300.0
U.S. OFFICE
Time Deposits [Line Items]
1 Year or Less	673.6
Over 1 Year to 2 Years	196.6
Over 2 Years to 3 Years	7.4
Over 3 Years to 4 Years	3.8
Over 4 Years to 5 Years	4.2
Over 5 Years	0.9
Total	886.5
NON-U.S. OFFICES
Time Deposits [Line Items]
1 Year or Less	1,018.9
Over 1 Year to 2 Years	0.0
Over 2 Years to 3 Years	0.0
Over 3 Years to 4 Years	0.0
Over 4 Years to 5 Years	0.0
Over 5 Years	0.0
Total	$ 1,018.9