Accumulated Other Comprehensive Income Loss - AOCI Rollforward (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 16,270
OCI, net of tax	$ 377	$ 412	804	$ 1,793
Ending balance	17,802	16,078	17,802	16,078
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	2,055	1,367	1,684	24
OCI before reclassifications	388	458	842	1,857
Amounts reclassified from AOCI	(12)	(57)	(95)	(113)
OCI, net of tax	376	401	747	1,744
Ending balance	2,431	1,768	2,431	1,768
Accumulated Other-than-Temporary Impairment Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(2)	(3)	(3)	(4)
OCI before reclassifications	0	0	1	1
Amounts reclassified from AOCI	0	0	0	0
OCI, net of tax	0	0	1	1
Ending balance	(2)	(3)	(2)	(3)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	48	11	9	(5)
OCI before reclassifications	(10)	8	37	27
Amounts reclassified from AOCI	(7)	(2)	(15)	(5)
OCI, net of tax	(17)	6	22	22
Ending balance	31	17	31	17
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	27	34	34	30
OCI before reclassifications	6	(4)	(1)	0
Amounts reclassified from AOCI	0	0	0	0
OCI, net of tax	6	(4)	(1)	0
Ending balance	33	30	33	30
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,649)	(1,607)	(1,672)	(1,624)
OCI before reclassifications	0	1	(1)	1
Amounts reclassified from AOCI	12	8	36	25
OCI, net of tax	12	9	35	26
Ending balance	(1,637)	(1,598)	(1,637)	(1,598)
AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	479	(198)	52	(1,579)
OCI before reclassifications	384	463	878	1,886
Amounts reclassified from AOCI	(7)	(51)	(74)	(93)
OCI, net of tax	377	412	804	1,793
Ending balance	$ 856	$ 214	$ 856	$ 214

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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