Investments in debt and equity securities (Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Cost Basis	$ 80
Due after one year through five years, Cost Basis	701
Due after five years through ten years, Cost Basis	148
Due after ten years, Cost Basis	32
Due in one year or less, Fair Value	80
Due after one year through five years, Fair Value	715
Due after five years through ten years, Fair Value	153
Due after ten years, Fair Value	33
Cost Basis	1,340	$ 1,171
Fair Value	1,365	1,151
Schedule of Debt and Equity Securities
Proceeds from Sale of Debt Securities, Available-for-sale	260	247	$ 930
Available-for-sale Securities, Proceeds, Gains and Losses
Debt Securities, Available-for-sale, Realized Gain	1	0	109
Debt Securities, Available-for-sale, Realized Loss	1	0	$ 5
Unrealized gain (loss) on equity securities held on report date	29	(25)
U.S. governmental agency mortgage-backed securities
Investments, Debt and Equity Securities [Abstract]
Cost Basis	327	301
Fair Value	331	297
Mortgage-backed securities - Residential
Investments, Debt and Equity Securities [Abstract]
Cost Basis	6	7
Fair Value	6	7
Mortgage-backed securities - Commercial
Investments, Debt and Equity Securities [Abstract]
Cost Basis	46	14
Fair Value	$ 47	$ 13