Escrow Deposits, Like-Kind Exchange Deposits and Trust Assets (Detail) (USD $) In Billions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Subsidiaries And Third Party Financial Institutions
Other Assets [Line Items]
Escrow deposits	$ 6.5	$ 4.7
First American Trust
Other Assets [Line Items]
Escrow deposits	2.1	1.6
Trust assets	3.0	3.0
Third Party Financial Institutions
Other Assets [Line Items]
Like-kind exchange funds	$ 2.2	$ 1.4