Stockholders' Equity and Earnings per Share - Changes in AOCI by Component, Net of Tax (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 11,442	$ 4,826	$ 9,122	$ 4,477
Total other comprehensive income (loss), net of taxes and reclassification adjustments	(14)	139	596	717
Ending balance	13,891	6,674	13,891	6,674
Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	1,048	443	438	(135)
Other comprehensive income (loss) before reclassifications	4	173	612	774
Amounts reclassified from accumulated other comprehensive income	(18)	(34)	(16)	(57)
Total other comprehensive income (loss), net of taxes and reclassification adjustments	(14)	139	596	717
Ending balance	1,034	582	1,034	582
AOCI related to available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	1,210	633	618	83
Other comprehensive income (loss) before reclassifications	4	173	610	776
Amounts reclassified from accumulated other comprehensive income	(20)	(49)	(34)	(102)
Total other comprehensive income (loss), net of taxes and reclassification adjustments	(16)	124	576	674
Ending balance	1,194	757	1,194	757
AOCI related to cash flow hedge relationships
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(220)	(277)	(244)	(315)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income	6	19	30	57
Total other comprehensive income (loss), net of taxes and reclassification adjustments	6	19	30	57
Ending balance	(214)	(258)	(214)	(258)
AOCI related to defined benefit plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	58	87	64	97
Other comprehensive income (loss) before reclassifications	0	0	2	(2)
Amounts reclassified from accumulated other comprehensive income	(4)	(4)	(12)	(12)
Total other comprehensive income (loss), net of taxes and reclassification adjustments	(4)	(4)	(10)	(14)
Ending balance	$ 54	$ 83	$ 54	$ 83

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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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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