Retirement and Benefit Plans (Targeted and Actual Weighted Average Asset Allocations by Plan Asset Category) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Total
Defined Benefit Plan Disclosure
Asset allocation by asset category	[1]	100.00%	100.00%
Targeted Range 0 to 55 Percent | Equity securities
Defined Benefit Plan Disclosure
Total equity securities	[1],[2]	$ 19	$ 67
Targeted Range 50 to 100 Percent | Fixed-income securities
Defined Benefit Plan Disclosure
Asset allocation by asset category	[1]	59.00%	23.00%
Targeted Range 0 to 5 Percent | Alternative strategies
Defined Benefit Plan Disclosure
Asset allocation by asset category	[1]		3.00%
Targeted Range 0 to 100 Percent | Cash
Defined Benefit Plan Disclosure
Asset allocation by asset category	[1]	22.00%	7.00%

[1] These reflect the targeted ranges for the year ended December 31, 2019.

[2] Includes mutual and exchange-traded funds.