Summary of Significant Accounting Policies, Accounting Changes (Details) - USD ($) $ in Millions	Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Changes [Abstract]
Shareholders' equity	$ 19,181		$ 21,930	$ 21,386	$ 24,566
Allowance for credit loss	40	[1]	0
Other assets	3,069		3,145
Other liabilities	4,623		5,111
Deferred non-insurance warranty acquisition expenses	3,068		2,840
Deferred non-insurance warranty revenue	4,023		3,779
Retained Earnings [Member]
Accounting Changes [Abstract]
Shareholders' equity	14,150		15,823	15,773	16,096
AOCI [Member]
Accounting Changes [Abstract]
Shareholders' equity	581		(68)	(880)	(26)
Cumulative Effect, Period of Adoption, Adjustment [Member]
Accounting Changes [Abstract]
Shareholders' equity			(5)		(91)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings [Member]
Accounting Changes [Abstract]
Shareholders' equity			(5)		(43)
Cumulative Effect, Period of Adoption, Adjustment [Member] | AOCI [Member]
Accounting Changes [Abstract]
Shareholders' equity					(28)
ASU 2016-13 [Member]
Accounting Changes [Abstract]
Allowance for credit loss			6
ASU 2016-13 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Accounting Changes [Abstract]
Allowance for credit loss	$ 6
ASU 2016-13 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings [Member]
Accounting Changes [Abstract]
Shareholders' equity			$ (5)
ASU 2016-02 [Member]
Accounting Changes [Abstract]
Other assets				642
Other liabilities				$ 642
ASU 2016-02 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | AOCI Pension Liability [Member]
Accounting Changes [Abstract]
Shareholders' equity					(130)
ASU 2016-02 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | AOCI Unrealized Gains (Losses) on Investments [Member]
Accounting Changes [Abstract]
Shareholders' equity					127
ASU 2014-09 [Member]
Accounting Changes [Abstract]
Deferred tax asset					23
Deferred non-insurance warranty acquisition expenses					(1,900)
Deferred non-insurance warranty revenue					(2,000)
ASU 2014-09 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings [Member]
Accounting Changes [Abstract]
Shareholders' equity					(62)
ASU 2016-01 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings [Member]
Accounting Changes [Abstract]
Shareholders' equity					25
ASU 2016-16 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings [Member]
Accounting Changes [Abstract]
Shareholders' equity					(9)
ASU 2018-02 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings [Member]
Accounting Changes [Abstract]
Shareholders' equity					$ 3

[1] On January 1, 2020, the Company adopted ASU 2016-13; see Note 1. The Unrealized OTTI Losses (Gains) column that tracked subsequent valuation changes on securities for which a credit loss had previously been recorded has been replaced with the Allowance for Credit Losses column. Prior period amounts were not adjusted for the adoption of this standard.