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Investment Information - Maturity profile of available for sale securities) (Details) - USD ($) $ in Thousands | Jun. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Estimated Fair Value |  |  |
Estimated Fair Value |  | $ 18,073,779 | $ 18,717,825
Amortized Cost |  |  |
Amortized cost |  | 17,764,783 | 18,143,305
Fixed maturities |  |  |
Estimated Fair Value |  |  |
Due in one year or less |  | 452,065 | 348,200
Due after one year through five years |  | 10,114,276 | 10,629,959
Due after five years through 10 years |  | 4,148,538 | 4,881,564
Due after 10 years |  | 371,337 | 482,180
Single maturity date |  | 15,086,216 | 16,341,903
Estimated Fair Value | [1] | 18,229,835 | 18,996,608
Amortized Cost |  |  |
Due in one year or less |  | 439,855 | 339,951
Due after one year through five years |  | 9,942,182 | 10,340,819
Due after five years through 10 years |  | 4,055,318 | 4,654,754
Due after 10 years |  | 355,241 | 448,139
Single maturity date |  | 14,792,596 | 15,783,663
Amortized cost | [1] | 17,920,162 | 18,421,669
Fixed maturities | Mortgage backed securities |  |  |
Estimated Fair Value |  |  |
Securities without single maturity date |  | 389,041 | 630,001
Estimated Fair Value |  | 389,041 | 630,001
Amortized Cost |  |  |
Securities without single maturity date |  | 388,309 | 626,368
Amortized cost | [1] | 388,309 | 626,368
Fixed maturities | Commercial mortgage backed securities |  |  |
Estimated Fair Value |  |  |
Securities without single maturity date |  | 266,733 | 389,900
Estimated Fair Value |  | 266,733 | 389,900
Amortized Cost |  |  |
Securities without single maturity date |  | 263,330 | 384,254
Amortized cost | [1] | 263,330 | 384,254
Fixed maturities | Asset backed securities |  |  |
Estimated Fair Value |  |  |
Securities without single maturity date |  | 2,487,845 | 1,634,804
Estimated Fair Value |  | 2,487,845 | 1,634,804
Amortized Cost |  |  |
Securities without single maturity date |  | 2,475,927 | 1,627,384
Amortized cost | [1] | $ 2,475,927 | $ 1,627,384
[1] | In securities lending transactions, the Company receives collateral in excess of the fair value of the fixed maturities pledged. For purposes of this table, the Company has excluded the collateral received under securities lending, at fair value and included the securities pledged under securities lending, at fair value. See “—Securities Lending Agreements.”

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