Separate Accounts (Separate Account Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Separate Account Investment [Line Items]
Separate account assets	$ 121,895,023	$ 119,188,485
U.S. Treasury securities and obligations of U.S. government authorities and agencies
Fair Value, Separate Account Investment [Line Items]
Separate account assets	3,226	2,954
U.S. corporate securities
Fair Value, Separate Account Investment [Line Items]
Separate account assets	8,510	9,504
Foreign corporate securities
Fair Value, Separate Account Investment [Line Items]
Separate account assets	1,857	1,763
Asset-backed securities
Fair Value, Separate Account Investment [Line Items]
Separate account assets	950	0
Mortgage-backed securities
Fair Value, Separate Account Investment [Line Items]
Separate account assets	180	186
Equity
Fair Value, Separate Account Investment [Line Items]
Separate account assets	76,205,304	72,614,821
Fixed Income
Fair Value, Separate Account Investment [Line Items]
Separate account assets	35,761,710	37,065,162
Other
Fair Value, Separate Account Investment [Line Items]
Separate account assets	4,275,354	4,101,661
Equity securities
Fair Value, Separate Account Investment [Line Items]
Separate account assets	114,738	104,159
Other invested assets
Fair Value, Separate Account Investment [Line Items]
Separate account assets	5,496,400	5,258,900
Short-term investments
Fair Value, Separate Account Investment [Line Items]
Separate account assets	2,367	2,126
Cash and cash equivalents
Fair Value, Separate Account Investment [Line Items]
Separate account assets	$ 24,427	$ 27,249