Investments - Amortized cost, gross unrealized gains and losses and fair value for fixed income securities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Schedule of Available for Sale Securities
Amortized cost	$ 62,267	$ 56,293
Gross unrealized, Gains	4,501	2,847
Gross unrealized, Losses	(217)	(96)
Fair value	66,551	59,044
U.S. government and agencies
Schedule of Available for Sale Securities
Amortized cost	2,737	4,971
Gross unrealized, Gains	114	141
Gross unrealized, Losses	(1)	(26)
Fair value	2,850	5,086
Municipal
Schedule of Available for Sale Securities
Amortized cost	8,948	8,080
Gross unrealized, Gains	769	551
Gross unrealized, Losses	(8)	(11)
Fair value	9,709	8,620
Corporate
Schedule of Available for Sale Securities
Amortized cost	48,317	41,090
Gross unrealized, Gains	3,554	2,035
Gross unrealized, Losses	(194)	(47)
Fair value	51,677	43,078
Foreign government
Schedule of Available for Sale Securities
Amortized cost	972	968
Gross unrealized, Gains	45	16
Gross unrealized, Losses	0	(5)
Fair value	1,017	979
ABS
Schedule of Available for Sale Securities
Amortized cost	1,211	860
Gross unrealized, Gains	9	8
Gross unrealized, Losses	(14)	(6)
Fair value	1,206	862
MBS
Schedule of Available for Sale Securities
Amortized cost	82	324
Gross unrealized, Gains	10	96
Gross unrealized, Losses	0	(1)
Fair value	$ 92	$ 419

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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