Insurance (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Analysis of changes in the liability for losses and loss adjustment expenses, net of reinsurance
Balance at beginning of period				$ 4,288				$ 4,129	$ 4,288		$ 4,129	$ 4,282
Provision for losses and LAE occurring in the current year									2,488		2,055	1,903
Net increase (decrease) in provision for claims of prior years	10	13	14	(31)	(5)	40	(22)	(28)	6		(15)	(30)
Total losses and LAE incurred									2,494		2,040	1,873
Payments for losses and LAE of:
Current year									(789)		(739)	(841)
Prior years									(1,340)		(1,131)	(1,185)
Total payments									(2,129)		(1,870)	(2,026)
Reserves of businesses acquired									1,028	[1]	0	0
Foreign currency translation and other									(36)		(11)	0
Balance at end of period	5,645				4,288				5,645		4,288	4,129
Add back reinsurance recoverables, net of allowance	2,227				2,122				2,227		2,122	2,716
Gross unpaid losses and LAE included in the Balance Sheet	$ 7,872				$ 6,410				$ 7,872		$ 6,410	$ 6,845

[1] Reflects the acquisition of Summit in April 2014 (see Note B — “Acquisitions and Sales of Businesses”).