Investments - Amortized cost, gross unrealized gains and losses and fair value for fixed income securities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available for Sale Securities
Amortized cost	$ 56,008	$ 57,134
Gross unrealized, Gains	2,567	993
Gross unrealized, Losses	(91)	(957)
Fair value	58,484	57,170
U.S. government and agencies
Schedule of Available for Sale Securities
Amortized cost	3,980	5,386
Gross unrealized, Gains	180	137
Gross unrealized, Losses	0	(6)
Fair value	4,160	5,517
Municipal
Schedule of Available for Sale Securities
Amortized cost	8,378	8,963
Gross unrealized, Gains	516	249
Gross unrealized, Losses	(3)	(43)
Fair value	8,891	9,169
Corporate
Schedule of Available for Sale Securities
Amortized cost	41,620	40,536
Gross unrealized, Gains	1,731	490
Gross unrealized, Losses	(78)	(890)
Fair value	43,273	40,136
Foreign government
Schedule of Available for Sale Securities
Amortized cost	766	739
Gross unrealized, Gains	26	13
Gross unrealized, Losses	(1)	(5)
Fair value	791	747
Asset-backed securities (“ABS”)
Schedule of Available for Sale Securities
Amortized cost	853	1,049
Gross unrealized, Gains	11	6
Gross unrealized, Losses	(5)	(10)
Fair value	859	1,045
Residential mortgage-backed securities (“RMBS”)
Schedule of Available for Sale Securities
Amortized cost	325	377
Gross unrealized, Gains	94	89
Gross unrealized, Losses	(1)	(2)
Fair value	418	464
Commercial mortgage-backed securities (“CMBS”)
Schedule of Available for Sale Securities
Amortized cost	65	63
Gross unrealized, Gains	8	8
Gross unrealized, Losses	(3)	(1)
Fair value	70	70
Redeemable preferred stock
Schedule of Available for Sale Securities
Amortized cost	21	21
Gross unrealized, Gains	1	1
Gross unrealized, Losses	0	0
Fair value	$ 22	$ 22