Supplemental financial information - Accumulated other comprehensive income (loss), net of taxes (AOCI) (Parenthetical) (Details) $ in Millions	Dec. 31, 2018 USD ($)
AOCI
Accumulated Other Comprehensive Income Loss [Line Items]
Cumulative effect of accounting changes	$ 30

Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

No definition available.

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