Investments in debt and equity securities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule of Debt and Equity Securities
Cost Basis	$ 1,340	$ 1,171
Unrealized Pretax Net Gains (Losses)	25	(20)
Fair Value	1,365	1,151
Government debt - U.S. treasury bonds
Schedule of Debt and Equity Securities
Cost Basis	9	9
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	9	9
Other U.S. and non-U.S. government bonds
Schedule of Debt and Equity Securities
Cost Basis	54	42
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	54	42
Corporate bonds
Schedule of Debt and Equity Securities
Cost Basis	836	735
Unrealized Pretax Net Gains (Losses)	20	(15)
Fair Value	856	720
Corporate bonds - Asset-backed securities
Schedule of Debt and Equity Securities
Cost Basis	62	63
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	62	63
U.S. governmental agency mortgage-backed securities
Schedule of Debt and Equity Securities
Cost Basis	327	301
Unrealized Pretax Net Gains (Losses)	4	(4)
Fair Value	331	297
Mortgage-backed securities - Residential
Schedule of Debt and Equity Securities
Cost Basis	6	7
Unrealized Pretax Net Gains (Losses)	0	0
Fair Value	6	7
Mortgage-backed securities - Commercial
Schedule of Debt and Equity Securities
Cost Basis	46	14
Unrealized Pretax Net Gains (Losses)	1	(1)
Fair Value	$ 47	$ 13