Investments (Portion Of Unrealized Gains And Losses On Equity Investmente Held) (Detail) - Equity Securities [Member] $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Gains (losses) on equity investments [Member]
Gain (Loss) on Investments [Line Items]
Realized investment gains (losses)	$ (4)
Gains (losses) on equity investments sold during the period [Member]
Gain (Loss) on Investments [Line Items]
Realized investment gains (losses)	1
Gains (losses) on equity investments still held at the end of the period [Member]
Gain (Loss) on Investments [Line Items]
Realized investment gains (losses)	$ (5)