Note 12 - Debt - Long-term Debt (Details) (Parentheticals)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Debentures, 8.875%, Due 2016 [Member]
Interest rate on debt	8.875%	8.875%
Debt maturity date	2016	2016
Debentures, 1.45%, Due 2017 [Member]
Interest rate on debt	1.45%	1.45%
Debt maturity date	2017	2017
Debentures, 1.5%, Due 2018 [Member]
Interest rate on debt	1.50%	1.50%
Debt maturity date	2018	2018
Debentures, 6.625%, Due 2019 [Member]
Interest rate on debt	6.625%	6.625%
Debt maturity date	2019	2019
Debentures, 4.25%, Due 2020 [Member]
Interest rate on debt	4.25%	4.25%
Debt maturity date	2020	2020
Debentures, 8.875%, Due 2021 [Member]
Interest rate on debt	8.875%	8.875%
Debt maturity date	2021	2021
Debentures, 2.9%, Due 2022 [Member]
Interest rate on debt	2.90%	2.90%
Debt maturity date	2022	2022
Debentures, 3.70%, due 2023 [Member]
Interest rate on debt	3.70%	3.70%
Debt maturity date	2023	2023
Medium-Term Notes, Average Rate 7.66%, Due Through 2023 [Member]
Interest rate on debt	7.66%	7.66%
Debt maturity date	2023	2023
Debentures, 7.00%, Due 2024 [Member]
Interest rate on debt	7.00%	7.00%
Debt maturity date	2024	2024
Debentures, 6.85%, Due 2029 [Member]
Interest rate on debt	6.85%	6.85%
Debt maturity date	2029	2029
Debentures, Callable, 7.25%, Due 2036 [Member]
Interest rate on debt	7.25%	7.25%
Debt maturity date	2036	2036
Debentures, 4.70%, Due 2037 [Member]
Interest rate on debt	4.70%	4.70%
Debt maturity date	2037	2037
Debentures, 5.75%, Due 2040 [Member]
Interest rate on debt	5.75%	5.75%
Debt maturity date	2040	2040
Debentures, 4.75%, Due 2042 [Member]
Interest rate on debt	4.75%	4.75%
Debt maturity date	2042	2042
Other, Average Rate 5.02%, Due Through 2042 [Member]
Interest rate on debt	5.02%	5.02%
Debt maturity date	2042	2042