Note 11 - Retirement Plans - Pension Plan Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined benefit plan, fair value of plan assets	$ 97	$ 84	$ 88
Fair Value, Inputs, Level 1 [Member]
Defined benefit plan, fair value of plan assets	81	67
Fair Value, Inputs, Level 2 [Member]
Defined benefit plan, fair value of plan assets	16	17
Fair Value, Inputs, Level 3 [Member]
Defined benefit plan, fair value of plan assets	0	0
Insurance General Account [Member]
Defined benefit plan, fair value of plan assets	16	17
Insurance General Account [Member] | Fair Value, Inputs, Level 1 [Member]
Defined benefit plan, fair value of plan assets	0	0
Insurance General Account [Member] | Fair Value, Inputs, Level 2 [Member]
Defined benefit plan, fair value of plan assets	16	17
Insurance General Account [Member] | Fair Value, Inputs, Level 3 [Member]
Defined benefit plan, fair value of plan assets	0	0
Cash and Cash Equivalents [Member]
Defined benefit plan, fair value of plan assets	2	1
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined benefit plan, fair value of plan assets	2	1
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined benefit plan, fair value of plan assets	0	0
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Defined benefit plan, fair value of plan assets	0	0
Equity Securities [Member]
Defined benefit plan, fair value of plan assets	46	39
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined benefit plan, fair value of plan assets	46	39
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined benefit plan, fair value of plan assets	0	0
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined benefit plan, fair value of plan assets	0	0
Fixed Income Securities [Member]
Defined benefit plan, fair value of plan assets	31	26
Fixed Income Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined benefit plan, fair value of plan assets	31	26
Fixed Income Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined benefit plan, fair value of plan assets	0	0
Fixed Income Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined benefit plan, fair value of plan assets	0	0
Real Estate [Member]
Defined benefit plan, fair value of plan assets	2	1
Real Estate [Member] | Fair Value, Inputs, Level 1 [Member]
Defined benefit plan, fair value of plan assets	2	1
Real Estate [Member] | Fair Value, Inputs, Level 2 [Member]
Defined benefit plan, fair value of plan assets	0	0
Real Estate [Member] | Fair Value, Inputs, Level 3 [Member]
Defined benefit plan, fair value of plan assets	$ 0	$ 0