Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pre-tax
Other comprehensive (loss) income	$ (22)	$ 347	$ (863)	$ 1,141
Tax
Other comprehensive (loss) income	6	(121)	183	(397)
After-tax
Other comprehensive (loss) income	(16)	226	(680)	744
Unrealized net holding gains and losses arising during the period, net of related offsets
Pre-tax
Unrealized net holding during the period	(116)	300	(1,103)	1,165
Less: reclassification adjustment	(26)	107	(129)	245
Other comprehensive (loss) income	(90)	193	(974)	920
Tax
Unrealized net holding during the period	25	(105)	233	(408)
Less: reclassification adjustment	5	(37)	27	(86)
Other comprehensive (loss) income	20	(68)	206	(322)
After-tax
Unrealized net holding during the period	(91)	195	(870)	757
Less: reclassification adjustment	(21)	70	(102)	159
Other comprehensive (loss) income	(70)	125	(768)	598
Unrealized foreign currency translation adjustments
Pre-tax
Other comprehensive (loss) income	(18)	43	(32)	55
Tax
Other comprehensive (loss) income	4	(15)	7	(19)
After-tax
Other comprehensive (loss) income	(14)	28	(25)	36
Unrecognized pension and other postretirement benefit cost
Pre-tax
Unrealized net holding during the period	0	(5)	4	(8)
Less: reclassification adjustment	(86)	(116)	(139)	(174)
Other comprehensive (loss) income	86	111	143	166
Tax
Unrealized net holding during the period	0	3	(1)	5
Less: reclassification adjustment	18	41	29	61
Other comprehensive (loss) income	(18)	(38)	(30)	(56)
After-tax
Unrealized net holding during the period	0	(2)	3	(3)
Less: reclassification adjustment	(68)	(75)	(110)	(113)
Other comprehensive (loss) income	$ 68	$ 73	$ 113	$ 110

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