Income taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Tax Credit Carryforward [Line Items]
Total U.S. repatriation tax commitments	$ 7,316,000,000
Remeasurement of net deferred and other tax liabilities, provisional income tax expense (benefit)	(1,200,000,000)
Provisional income tax expense (benefit)	6,100,000,000
Significant change in UTB is reasonably possible, amount of unrecorded benefit	63,000,000
Interest and penalties related to unrecognized tax benefits recognized in income tax provision	56,000,000	$ 125,000,000	$ 17,000,000
Accrued interest and penalties associated with unrecognized tax benefits	332,000,000	276,000,000
Income taxes paid	$ 1,500,000,000	$ 1,100,000,000	$ 919,000,000
Puerto Rico [Member]
Tax Credit Carryforward [Line Items]
Tax rate	4.00%
Domestic [Member]
Tax Credit Carryforward [Line Items]
Tax credit carryforwards available to reduce income taxes	$ 20,000,000
Tax credit carryforwards, valuation allowance	0
NOL carryforwards available to reduce income taxes	146,000,000
NOL carryforwards, valuation allowance	6,000,000
State [Member]
Tax Credit Carryforward [Line Items]
Tax credit carryforwards available to reduce income taxes	524,000,000
Tax credit carryforwards, valuation allowance	392,000,000
NOL carryforwards available to reduce income taxes	425,000,000
NOL carryforwards, valuation allowance	400,000,000
Foreign [Member]
Tax Credit Carryforward [Line Items]
NOL carryforwards available to reduce income taxes	2,000,000,000
NOL carryforwards, valuation allowance	819,000,000
NOLs with no valuation allowance and no expiration	678,000,000
Expiration in tax years beginning 2022 [Member] | State [Member]
Tax Credit Carryforward [Line Items]
Tax credit carryforwards, valuation allowance	0
Operating Losses That Expire Between 2020 and 2035 [Member] | Domestic [Member]
Tax Credit Carryforward [Line Items]
NOL carryforwards, valuation allowance	0
Operating Losses That Expire Between 2018 and 2032 [Member] | State [Member]
Tax Credit Carryforward [Line Items]
NOL carryforwards, valuation allowance	0
Operating Losses With No Expiry or Expiry Beginning 2018 [Member] | Foreign [Member]
Tax Credit Carryforward [Line Items]
NOL carryforwards, valuation allowance	$ 0