Benefit Plans - Plan Assets Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) (Pension Benefits [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Balance at January 1	$ 500	$ 486
Actual Return on Assets Still Held at December 31	40	66
Actual Return on Assets Sold During the Year Ended December 31	1	(1)
Net Purchases, Sales, and Settlements	(70)	(35)
Net Transfers In (Out) of Level 3		(16)
Balance at December 31	471	500
Corporate and Other Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance at January 1		11
Actual Return on Assets Still Held at December 31		(1)
Net Purchases, Sales, and Settlements		5
Balance at December 31	15	15
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance at January 1	8	5
Actual Return on Assets Still Held at December 31		3
Net Purchases, Sales, and Settlements	(8)
Balance at December 31		8
Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance at January 1	352	391
Actual Return on Assets Still Held at December 31	21	62
Net Purchases, Sales, and Settlements	(40)	(85)
Net Transfers In (Out) of Level 3		(16)
Balance at December 31	333	352
Private Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance at January 1	125	69
Actual Return on Assets Still Held at December 31	19	2
Actual Return on Assets Sold During the Year Ended December 31	1	(1)
Net Purchases, Sales, and Settlements	(22)	55
Balance at December 31	123	125
Investment Contracts with Insurance Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance at January 1		10
Net Purchases, Sales, and Settlements		(10)
Limited Partnership Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance at January 1	477	460
Actual Return on Assets Still Held at December 31	40	64
Actual Return on Assets Sold During the Year Ended December 31	1	(1)
Net Purchases, Sales, and Settlements	(62)	(30)
Net Transfers In (Out) of Level 3		(16)
Balance at December 31	$ 456	$ 477