Investments - Amortized cost, gross unrealized gains and losses and fair value for fixed income securities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Schedule of Available for Sale Securities
Amortized cost, net	$ 38,811	$ 40,034
Gross unrealized, Gains	1,330	2,563
Gross unrealized, Losses	(152)	(32)
Fixed income securities, at fair value	39,989	42,565
U.S. government and agencies
Schedule of Available for Sale Securities
Amortized cost, net	3,035	2,058
Gross unrealized, Gains	22	50
Gross unrealized, Losses	(15)	(1)
Fixed income securities, at fair value	3,042	2,107
Municipal
Schedule of Available for Sale Securities
Amortized cost, net	7,117	7,100
Gross unrealized, Gains	318	480
Gross unrealized, Losses	(18)	(2)
Fixed income securities, at fair value	7,417	7,578
Corporate
Schedule of Available for Sale Securities
Amortized cost, net	26,515	29,057
Gross unrealized, Gains	963	1,986
Gross unrealized, Losses	(111)	(26)
Fixed income securities, at fair value	27,367	31,017
Foreign government
Schedule of Available for Sale Securities
Amortized cost, net	1,054	921
Gross unrealized, Gains	12	37
Gross unrealized, Losses	(7)	0
Fixed income securities, at fair value	1,059	958
ABS
Schedule of Available for Sale Securities
Amortized cost, net	1,057	840
Gross unrealized, Gains	14	9
Gross unrealized, Losses	(1)	(3)
Fixed income securities, at fair value	1,070	846
MBS
Schedule of Available for Sale Securities
Amortized cost, net	33	58
Gross unrealized, Gains	1	1
Gross unrealized, Losses	0	0
Fixed income securities, at fair value	$ 34	$ 59

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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