Financial Instruments, Derivatives and Hedging Activities - Interest rate hedging (Details) - 4.625% senior notes due November 1, 2020 $ in Millions	Dec. 31, 2020 USD ($)
Financial instruments, derivatives and hedging activities
Principal amount	$ 400
Debt, fixed interest rate (as a percent)	4.625%
Fair Value Hedging \| Interest Rate Swap
Financial instruments, derivatives and hedging activities
Principal amount	$ 200

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant