Non-Insurance Revenues from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Unearned revenue associated with outstanding non-insurance warrany product and service contracts	$ 3,000	$ 2,900
Contract with customer, liability, revenue recognized	222
Capitalized commission costs	2,200
Deferred commission costs	17
Amortization of deferred sales commissions	$ 157
Minimum
Disaggregation of Revenue [Line Items]
Warranty contract duration	1 month
Maximum
Disaggregation of Revenue [Line Items]
Warranty contract duration	10 years