Hedging transactions and derivative financial instruments Hedging transactions and derivative financial instruments (Summary of Notional Values and Pretax Impact in Fair Values) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Nov. 30, 2019	Jun. 30, 2019	Jan. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Derivative and nonderivative, original notional amount	$ 13,000.9
Derivative and nonderivative, notional amount	11,275.9
Gain (loss) recognized in OCI on derivatives and nonderivatives	4.8
Net investment hedging | Foreign currency contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, original notional amount	1,875.0			$ 1,900.0
Derivative, notional amount	1,000.0
Gain (loss) recognized in OCI on derivatives	24.1
Net investment hedging | Foreign currency denominated debt
Derivative Instruments, Gain (Loss) [Line Items]
Nonderivative hedging instruments	6,275.9
Gain (loss) recognized in OCI on nonderivatives	129.9
Cash flow hedging | Foreign currency contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, original notional amount	4,000.0	$ 4,000.0
Derivative, notional amount	4,000.0
Gain (loss) recognized in OCI on derivatives	(111.7)
Cash flow hedging | Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, original notional amount	850.0		$ 850.0
Derivative, notional amount	0.0
Gain (loss) recognized in OCI on derivatives	$ (37.5)