Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	$ 577,000,000	$ 655,000,000	$ 703,000,000
Impaired loans	8,000,000		8,000,000
Goodwill	1,060,000,000	1,060,000,000	1,057,000,000
Level 3 [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans	8,000,000		8,000,000
Level 3 [Member] | Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Other investments	24,000,000	50,000,000	70,000,000
Level 3 [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans	8,000,000		8,000,000
Goodwill	$ 1,060,000,000	1,060,000,000	$ 1,057,000,000
Level 3 [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Impaired loans		$ 1,000,000
Level 3 [Member] | Impaired Loans [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value measurement, valuation technique	Fair value of underlying collateral
Level 3 [Member] | Goodwill [Member] | Nonrecurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value measurement, valuation technique	Discounted cash flow and market data
Level 3 [Member] | Other Investments [Member] | Recurring [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value measurement, valuation technique	Individual analysis of the condition of each investment
Level 3 [Member] | Discount [Member] | Recurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs			8.00%
Level 3 [Member] | Discount [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	35.00%	34.00%	64.00%
Level 3 [Member] | Discount [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	0.00%	0.00%	0.00%
Level 3 [Member] | Discount [Member] | Nonrecurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	6.00%	15.00%	35.00%
Level 3 [Member] | EBITDA Multiple [Member] | Recurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	6.30%		6.00%
Level 3 [Member] | EBITDA Multiple [Member] | Recurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	5.30%		5.40%
Level 3 [Member] | EBITDA Multiple [Member] | Recurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	6.20%	5.40%	5.50%
Level 3 [Member] | EBITDA Multiple (Where Applicable) [Member] | Recurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		6.70%	6.80%
Level 3 [Member] | EBITDA Multiple (Where Applicable) [Member] | Recurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs		5.40%	6.00%
Level 3 [Member] | EBITDA Multiple (Where Applicable) [Member] | Recurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	6.30%	6.60%	6.70%
Level 3 [Member] | Earnings Multiple of Peers [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input	17.80%	17.80%	15.90%
Level 3 [Member] | Earnings Multiple of Peers [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input	10.30%	10.30%	11.40%
Level 3 [Member] | Earnings Multiple of Peers [Member] | Nonrecurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input	12.79%	12.79%	12.92%
Level 3 [Member] | Equity Multiple of Peers [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input	1.56%	1.56%	1.22%
Level 3 [Member] | Equity Multiple of Peers [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input	1.25%	1.25%	1.20%
Level 3 [Member] | Equity Multiple of Peers [Member] | Nonrecurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Significant unobservable input	1.43%	1.43%	1.21%
Level 3 [Member] | Control Premium [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	30.00%	30.00%	30.00%
Level 3 [Member] | Control Premium [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	10.00%	10.00%	10.00%
Level 3 [Member] | Control Premium [Member] | Nonrecurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	19.18%	19.18%	19.70%
Level 3 [Member] | Weighted-average Cost Of Capital [Member] | Nonrecurring [Member] | Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	13.00%	13.00%	14.00%
Level 3 [Member] | Weighted-average Cost Of Capital [Member] | Nonrecurring [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	12.00%	12.00%	13.00%
Level 3 [Member] | Weighted-average Cost Of Capital [Member] | Nonrecurring [Member] | Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Percentage of significant unobservable inputs	12.54%	12.54%	13.52%