Investments (Tables)

12 Months Ended

Dec. 31, 2017

Regulated Entity, Other Assets, Noncurrent [Abstract]

Amortized Cost and Fair Value of the Trust Investments

The following table sets forth amortized cost and fair value of the trust investments (see Note 4 for a discussion of fair value of the trust investments):

	Longest Maturity Date	Amortized Cost				Fair Value
		December 31,
(in millions)		2017		2016		2017		2016
Stocks	—	$	236	$	319	$	1,596	$	1,547
Municipal bonds	2054	643		659		768		766
U.S. government and agency securities	2067	1,235		1,131		1,319		1,191
Corporate bonds	2057	579		600		643		659
Short-term investments and receivables/payables1	One-year	110		75		114		79
Total		$	2,803	$	2,784	$	4,440	$	4,242

¹ Short-term investments include $29 million and $114 million of repurchase agreements payable by financial institutions which earn interest, are fully secured by U.S. Treasury securities and mature by January 2, 2018 and January 4, 2017 as of December 31, 2017 and 2016, respectively.