Insurance Premiums (Undiscounted Future Amount Of Premiums Expected To Be Collected And Period Which Those Collections Are Expected To Occur) (Detail) $ in Millions	Dec. 31, 2017 USD ($)
Insurance Premiums [Abstract]
Three months ending, March 31, 2018, Expected Collection of Premiums	$ 5
Three months ending, June 30, 2018, Expected Collection of Premiums	15
Three months ending, September 30, 2018, Expected Collection of Premiums	7
Three months ending, December 31, 2018, Expected Collection of Premiums	14
Twelve months ending, December 31, 2019, Expected Collection of Premiums	38
Twelve months ending, December 31, 2020, Expected Collection of Premiums	35
Twelve months ending, December 31, 2021, Expected Collection of Premiums	32
Twelve months ending, December 31, 2022, Expected Collection of Premiums	28
Five years ending, December 31, 2027, Expected Collection of Premiums	120
Five years ending, December 31, 2032, Expected Collection of Premiums	71
Five years ending, December 31, 2037 and thereafter, Expected Collection of Premiums	81
Total, Expected Collection of Premiums	$ 446