Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pre-tax
Other comprehensive income (loss)	$ 1,227	$ (737)
Tax
Other comprehensive income (loss)	(260)	156
After-tax
Other comprehensive income (loss)	967	(581)
Unrealized net holding gains and losses arising during the period, net of related offsets
Pre-tax
Unrealized net holding during the period	1,287	(740)
Less: reclassification adjustment	51	(25)
Other comprehensive income (loss)	1,236	(715)
Tax
Unrealized net holding during the period	(273)	155
Less: reclassification adjustment	(11)	5
Other comprehensive income (loss)	(262)	150
After-tax
Unrealized net holding during the period	1,014	(585)
Less: reclassification adjustment	40	(20)
Other comprehensive income (loss)	974	(565)
Unrealized foreign currency translation adjustments
Pre-tax
Other comprehensive income (loss)	6	(3)
Tax
Other comprehensive income (loss)	(1)	1
After-tax
Other comprehensive income (loss)	5	(2)
Unamortized pension and other postretirement prior service credit
Pre-tax
Unrealized net holding during the period	0	0
Less: reclassification adjustment	15	19
Other comprehensive income (loss)	(15)	(19)
Tax
Unrealized net holding during the period	0	0
Less: reclassification adjustment	(3)	(5)
Other comprehensive income (loss)	3	5
After-tax
Unrealized net holding during the period	0	0
Less: reclassification adjustment	12	14
Other comprehensive income (loss)	$ (12)	$ (14)