Note 12 - Debt (Details) - Long-term Debt (Parentheticals)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Debentures, 8.875%, Due 2016 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	8.875%	8.875%
Debt maturity date	2016	2016
Debentures, 1.45%, Due 2017 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	1.45%	1.45%
Debt maturity date	2017	2017
Debentures 1.5%, Due 2018 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	1.50%
Debt maturity date	2018
Debentures 6.625% Due 2019 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	6.625%	6.625%
Debt maturity date	2019	2019
Debentures 4.25% Due 2020 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	4.25%	4.25%
Debt maturity date	2020	2020
Debentures, 8.875%, Due 2021 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	8.875%	8.875%
Debt maturity date	2021	2021
Debentures 2.9%, Due 2022 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	2.90%
Debt maturity date	2022
Debentures, 3.70%, due 2023 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	3.70%	3.70%
Debt maturity date	2023	2023
Medium Term Notes Average Rate 7.66% Due Through 2023 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	7.66%	7.66%
Debt maturity date	2023	2023
Debentures 7.00% Due 2024 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	7.00%	7.00%
Debt maturity date	2024	2024
Debentures 6.85% Due 2029 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	6.85%	6.85%
Debt maturity date	2029	2029
Debentures Callable 7.25% Due 2036 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	7.25%	7.25%
Debt maturity date	2036	2036
Debentures, 4.70%, Due 2037 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	4.70%	4.70%
Debt maturity date	2037	2037
Debentures 5.75% Due 2040 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	5.75%	5.75%
Debt maturity date	2040	2040
Debentures, 4.75%, Due 2042 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	4.75%	4.75%
Debt maturity date	2042	2042
Other Average Rate 5.02%, Due Through 2042 [Member]
Note 12 - Debt (Details) - Long-term Debt (Parentheticals) [Line Items]
Interest rate on debt	5.02%	5.02%
Debt maturity date	2042	2042