Investment Securities (Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency) (Details) $ in Millions	Dec. 31, 2019 USD ($) fund	Dec. 31, 2018 USD ($)
Private equity funds
Investment securities
Number of Investments Held | fund	12
Trading security, fair value	$ 106.5
Hedge funds
Investment securities
Number of Investments Held | fund	1
Total private equity funds and hedge funds included in other long-term investments
Investment securities
Other long-term investments largest single investment	$ 54.6	$ 54.3
Trading security, fair value	161.1	146.1
Fair value unfunded commitments	50.2	76.7
Private equity funds | Private equity funds
Investment securities
Trading security, fair value	106.5	91.8
Fair value unfunded commitments	50.2	76.7
Private equity funds | Manufacturing/Industrial
Investment securities
Trading security, fair value	57.7	42.9
Fair value unfunded commitments	4.1	10.5
Private equity funds | Aerospace/Defense/Government
Investment securities
Trading security, fair value	33.8	27.6
Fair value unfunded commitments	23.3	34.9
Private equity funds | Financial services
Investment securities
Trading security, fair value	15.0	8.3
Fair value unfunded commitments	22.8	13.6
Private equity funds | Direct lending
Investment securities
Trading security, fair value	0.0	13.0
Fair value unfunded commitments	0.0	17.7
Hedge funds | Hedge funds
Investment securities
Trading security, fair value	54.6	54.3
Fair value unfunded commitments	0.0	0.0
Hedge funds | Hedge Fund, Long/ Short Equity Banks and Financial
Investment securities
Trading security, fair value	54.6	54.3
Fair value unfunded commitments	$ 0.0	$ 0.0