Insurance (Rollforward of Unpaid Claims) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability for Claims and Claims Adjustment Expense [Line Items]
Balance at January 1,	$ 17,094	$ 16,157	$ 9,669
Less: Reinsurance recoverables	2,198	1,968	476
Net Balance at January 1,	14,896	14,189	14,012
Incurred related to:
Current year	24,571	24,370	24,011
Prior years	454	133	382
Total incurred	25,025	24,503	24,393
Paid related to:
Current year	(18,757)	(18,525)	(18,696)
Prior years	(5,708)	(5,271)	(5,520)
Total paid	(24,465)	(23,796)	(24,216)
Net Balance at December 31,	15,456	14,896	14,189
Add: Reinsurance recoverables	2,332	2,198	1,968
Balance at December 31,	17,788	17,094	16,157
Accounting Standard update 2015-09
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Balance at January 1,	0	0	4,819
Paid related to:
Net Balance at December 31,		0	0
Previously Reported
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Balance at January 1,	$ 14,896	14,189	9,193
Paid related to:
Net Balance at December 31,		$ 14,896	$ 14,189