Investment securities (Investments Classified by Credit Rating) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	$ 1,253	$ 1,568
Debt Securities, held-to-maturity, less than 12 Months, fair value		283
Debt securities, held-to-maturity, unrealized loss, less than 12 Months		(6)
Debt Securities, held-to-maturity, 12 Months or Longer, fair value		3
Debt securities, held-to-maturity, unrealized loss, 12 months or longer		0
Agency mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	1,253
Debt Securities, held-to-maturity, less than 12 Months, fair value		283
Debt securities, held-to-maturity, unrealized loss, less than 12 Months		(6)
Debt Securities, held-to-maturity, 12 Months or Longer, fair value		0
Debt securities, held-to-maturity, unrealized loss, 12 months or longer		0
Asset-backed
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, held-to-maturity, less than 12 Months, fair value		0
Debt securities, held-to-maturity, unrealized loss, less than 12 Months		0
Debt Securities, held-to-maturity, 12 Months or Longer, fair value		3
Debt securities, held-to-maturity, unrealized loss, 12 months or longer		$ 0
AA Rating
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	1,253
AA Rating \| Agency mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	$ 1,253

Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for less than 12 months.

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