Investments - Amortized cost, gross unrealized gains and losses and fair value for fixed income securities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Schedule of Available for Sale Securities
Amortized cost, net	$ 39,437	$ 40,034
Gross unrealized, Gains	1,409	2,563
Gross unrealized, Losses	(252)	(32)
Fixed income securities, at fair value	40,594	42,565
U.S. government and agencies
Schedule of Available for Sale Securities
Amortized cost, net	3,103	2,058
Gross unrealized, Gains	26	50
Gross unrealized, Losses	(19)	(1)
Fixed income securities, at fair value	3,110	2,107
Municipal
Schedule of Available for Sale Securities
Amortized cost, net	7,226	7,100
Gross unrealized, Gains	310	480
Gross unrealized, Losses	(36)	(2)
Fixed income securities, at fair value	7,500	7,578
Corporate
Schedule of Available for Sale Securities
Amortized cost, net	27,145	29,057
Gross unrealized, Gains	1,045	1,986
Gross unrealized, Losses	(187)	(26)
Fixed income securities, at fair value	28,003	31,017
Foreign government
Schedule of Available for Sale Securities
Amortized cost, net	977	921
Gross unrealized, Gains	16	37
Gross unrealized, Losses	(8)	0
Fixed income securities, at fair value	985	958
ABS
Schedule of Available for Sale Securities
Amortized cost, net	934	840
Gross unrealized, Gains	11	9
Gross unrealized, Losses	(2)	(3)
Fixed income securities, at fair value	943	846
MBS
Schedule of Available for Sale Securities
Amortized cost, net	52	58
Gross unrealized, Gains	1	1
Gross unrealized, Losses	0	0
Fixed income securities, at fair value	$ 53	$ 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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