Investment Securities - Fair Value of Hedge Funds and Private Equity Funds (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Hedge and private equity funds included in other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 118.2	$ 161.1
Unfunded Commitments	41.5	50.2
Private equity funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	118.2	106.5
Unfunded Commitments	41.5	50.2
Private equity funds | Aerospace/Defense/Government
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	59.4	33.8
Unfunded Commitments	16.1	23.3
Private equity funds | Manufacturing/Industrial
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	39.8	57.7
Unfunded Commitments	2.0	4.1
Private equity funds | Financial services
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	19.0	15.0
Unfunded Commitments	23.4	22.8
Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	0.0	54.6
Unfunded Commitments	0.0	0.0
Hedge funds | Long/short banks and financials
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	0.0	54.6
Unfunded Commitments	$ 0.0	$ 0.0