Income Taxes - Reconciliation of income tax percentage (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Statutory federal income tax rate - expense	21.00%	21.00%	35.00%
Tax credits	(1.90%)	(3.20%)	(1.70%)
Dividends received deduction	(0.50%)	(0.70%)	(0.60%)
State income taxes	0.50%	1.50%	0.60%
Adjustments to prior year tax liabilities	0.20%	(0.30%)	(0.30%)
Non-deductible expenses	0.10%	0.00%	0.10%
Tax Legislation benefit	0.00%	(14.00%)	(71.80%)
Other	0.00%	0.10%	0.00%
Effective Income Tax Rate Reconciliation, Percent	19.40%	4.40%	(38.70%)