Investment Securities - Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency (Details) $ in Millions	Dec. 31, 2021 USD ($) fund	Dec. 31, 2020 USD ($)
Total private equity funds and hedge funds included in other long-term investments
Investment securities
Other long-term investments largest single investment	$ 31.3	$ 29.1
Trading security, fair value	153.8	121.2
Fair value unfunded commitments	$ 44.0	45.7
Private equity funds
Investment securities
Number of investments | fund	12
Trading security, fair value	$ 141.8	121.2
Fair value unfunded commitments	44.0	45.7
Private equity funds | Aerospace/Defense/Government
Investment securities
Trading security, fair value	69.8	69.1
Fair value unfunded commitments	11.8	15.3
Private equity funds | Financial services
Investment securities
Trading security, fair value	67.7	23.5
Fair value unfunded commitments	29.3	30.4
Private equity funds | Real Estate
Investment securities
Trading security, fair value	4.3	0.0
Fair value unfunded commitments	2.9	0.0
Private equity funds | Manufacturing/Industrial
Investment securities
Trading security, fair value	0.0	28.6
Fair value unfunded commitments	$ 0.0	0.0
Hedge funds
Investment securities
Number of investments | fund	1
Trading security, fair value	$ 12.0	0.0
Fair value unfunded commitments	0.0	0.0
Hedge funds | European small/mid cap
Investment securities
Trading security, fair value	12.0	0.0
Fair value unfunded commitments	$ 0.0	$ 0.0