Investment Securities - Fair Value of Hedge Funds and Private Equity Funds (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Hedge and private equity funds included in other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 144.2	$ 121.2
Unfunded Commitments	46.5	45.7
Private equity funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	132.0	121.2
Unfunded Commitments	46.5	45.7
Private equity funds | Aerospace/Defense/Government
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	63.9	69.1
Unfunded Commitments	14.0	15.3
Private equity funds | Financial services
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	63.2	23.5
Unfunded Commitments	29.6	30.4
Private equity funds | Real Estate
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	4.8	0.0
Unfunded Commitments	2.9	0.0
Private equity funds | Manufacturing/Industrial
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	0.1	28.6
Unfunded Commitments	0.0	0.0
Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	12.2	0.0
Unfunded Commitments	0.0	0.0
Hedge funds | European small/mid cap
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	12.2	0.0
Unfunded Commitments	$ 0.0	$ 0.0